The Luftwaffe absolutely flew ground attack missions on the Western Front.

A German soldiers' joke that comes to mind here: "When a silver airplane flies over, it's American. When a green airplane flies by, it's British. When an in invisible plane flies over, that's the Luftwaffe."

German air attacks were very rare on the Western Front from 1944-1945. The Luftwaffe was largely a spent force in the West by then. At this point, the Luftwaffe, like the rest of the German armed force, was fighting a war on three fronts in Western Europe, Italy, and Eastern Europe. Plus, the Luftwaffe had to fight off USAAF daytime bombing and RAF night raids. The defense of the Reich from air attack was particularly demanding of fighter aircraft, aircrew, and precious fuel. Most specialized ground attack formations were concentrated on the collapsing the Eastern Front. As a result, the Luftwaffe did not have the resources to launch many close air support or battlefield interdiction sorties (i.e. strafing rear areas and roads) on the Western Front in 1944-1945. Fuel in particular was a major constraint on all operations.

Hauptmann Roderich Cescotti of JG 301 recalled the problems his FW 190 D unit faced in early 1945:

Getting fuel for the fighters was not ao much a logistics operations, more an intelligence battle. We would send tankers on circuitous journeys, picking up 5,000 litres in one place, 2,500 litres at another; sometimes it might take as long as a week to collect the twenty tons of fuel needed for a single fighter operation.

But just because German air attacks were rare doesn't mean they didn't happen.

The Luftwaffe was still active on the Western Front during the fighting of late 1944 and early 1945. Many sorties were defensive counter-air missions aimed at shooting down Allied fighter-bombers and bombers attacking German forward areas. Ground attack sorties were also flown, usually by attack aircraft from dedicated Schalchtgruppen ("attack groups").

In October 1943, the Luftwaffe had dramatically expanded the Schlacht units. Stukageschwader units were redesignated as Schlachtgeschwader, and dedicated ground attack aircraft like the Hs 129 and Fw 190 F (an up-armored variant of the Fw 190) began to reach thr front in greater numbers.

Military Aviation History has a relevant video here on "How the FW 190 became a fighter-bomber." - https://m.youtube.com/watch?v=Wnlf3IK8a8I

On D-Day in June 1944, the Luftwaffe had only one dedicated ground attack unit in Occupied Euopre: part of Schlachtgeschwader 4 (Attack Wing 4). The Fw 190 pilots of III/SG 4 (3rd Group, Attack Wing 4) contested the Allies as best they could by strafing and bombing, but they were quickly overwhelmed. After losing over 20 aircraft in just two weeks (nearly 25 percent losses), III/SG 4 had to be withdrawn.

Efforts to rush more aircraft to the Normandy area often ended in disaster. Of the dozen Stukas sent by Schlachtgeschwader 101 to the Normandy area on June 8th, 1944, only one survived a ferocious attack by Allied fighters.

Other German units also mounted ground attack missions. The Fw 190 Jabo fighter-bombers of I Gruppe of Schnellkampfgeschwader 10 (SKG 10) abandoned their cross-Channel bombing raids in favor of naval attack and ground attack missions in France. Flying two to five missions a day, the pilots used night and bad weather to cover many of their attacks, occasionally making low-light or daylight raids. By mid-August, they'd flown over 3,000 sorties, losing 20 planes in the process. But the Allied breakout threatened its bases, forcing it to pull back with just 6 serviceable aircraft remaining.

As the Allies continued to advance across Western Europe, the Luftwaffe continued to launch ground attacks, although Allied air superiority forced more and raids to be launched at night or during bad weather during daylight. This was the only way obsolete aircraft like the Ju 87 Stuka hadd any chance of surviving in the face of Allied air superiority. In early Decembe 1944, Stuka units made a rare daylight strike on American armor in the Huertegen Forest. Otherwise, the Stukas focused on night raids.

The Luftwaffe summoned the last of its strength in the West during the Battle of the Bulge in December 1944. On December 16th, the Luftwaffe managed to get nearly 500 aircraft airborne to support the offensive, despite the bad weather.

On December 16, over fifty Stukas attacked U.S. troops near Monschau in five waves. To illuminate their night attacks, the bombers dropped flares, then bombed and strafed, albeit to limited effect. Throughout the rest of the Bulge fighting, the Stukas would launch similar night attacks, albeit on a smaller scale. The American troops rushing to reinforce the Bulge were singled out for special attention, although the air attacks were generally little more than a nuisance to the G.Is.

The Germans had also moved the entirety of Schlachtgeschwader 4 and its Fw 190s from the Eastern Front, nearly a hundred aircraft in all. The Normandy veterans of III/SG 4 had been re-equipped with rocket-firing Fw 190s armed with Panzerblitz anti-tank rocket.

Initially, Luftwaffe commanders held SG 4 reserve, planning to use SG 4 to help German troops cross the Meuse River and dash for the Channel ports. However, the German advance stalled and the attack aircraft had to be retasked. On December 18th, they made bomb, rocket, and cannon attack against American forces in St. Vith. On Christmas Eve and Boxing Day, SG 4 struck Bastogne, losing multiple aircraft to determined ground fire and a tussle with RAF Typhoons while they returned to base. A strike on the 27th went even worse, as SG 4 accidentally bombed German territory after failing to find their target.

Don Burgett, a former squad leader in the 101st Airborne Division, talks about coming under German air attack here. https://m.youtube.com/watch?v=SFPqDYEFSNQ

Other Luftwaffe units were similarly-active over the Bulge l, trying to shoot down Allied aircraft and attack Allied troops. These missions extracted a heavy toll on the Luftwaffe. Outnumbered and Often under-trained pilots took heavy losses from Allied fighters and AA guns. In the eight flying days between Dceemebr 17th and December 27th, almost 650 aircraft were lost, along with nearly 350 pilots.

On New Year's Day 1945, the Luftwaffe launched its last great airstrike of the war. Virtually every single German day fighter and fighter-bomber on the Western Front, just over 1,000 aircraft were sent to attack the Allies. Operation Bodenplatte aimed to give the Luftwaffe superiority over the Western Front in one swoop by destroying 16 key Allied air bases in Belgium, the Netherlands and France. The raid was a disaster. Although surprised, the Allies quickly reacted. AA guns filled the skies with tracers and fighters scrambled to intercept their attackers. The Germans lost nearly 250 aircraft. Even worse, more than 200 pilots killed or captured, including large numbers of highly experienced senior officers. Many Geschwader lost 25-40% of their staff officers. SG 4's commanding officer Oberst (Colonel) Alfred Druschel, a veteran of over 800 missions on the Eastern Front and a holder of the Knight's Cross with Swords and Oak Leaves, died before he even got to the target, after AA fire bagged him and three wingmates.

From that point on, German attack sorties in the West were flown almost exclusively at night or in bad weather. A few fighter (JG) and attack (SG) unit made daylight strikes until the end if the war, but these were extremely perilous missions for the young, green fighter pilots ordered to fly them.

Typical German ground attack tactics were fairly simple. Fw 190 attack units tended to make a shallow gliding attack in a line-astern formation. However, ground fire sometimes made this approach suicidal. At Anzio in early 1944, Fw 190 pilots had to resort to steep 65-degree dive-bombing attacks to avoid ground fire.

By the end of the war, attacking Allied columns had become a perilous endeavour. One young pilot recalled the advice he was given.

"Don't fly straight down the road when strafing the convoys. With all their flak, that's asking for trouble. Zig-zag backwards and forwards along their route, and use the protection of the trees. You can give them a burst each time you fly across the road, and that way you cut the return fire by a good half - they don't like shooting across the trees [by the side of the road] for fear of premature s and ricochets."

As for Allied friendly fire? It absolutely happened and was a considerable cause for concern amongst front-line troops. Western Allied vehicles were marked with large white stars and often carried large orange marker panels or national flags to ID them to pilots. However, these signals were not enough to ward off trigger-happy, confused, or inexperienced pilots.

While in Sicily during 1943, II Corps commander Lieutenant General Omar Bradley, was strafed by USAAF A-36s Apaches in Sicily. Even though the column showed yellow smoke to identify themselves, the Apaches kept attacking. American troops eventually returned fire and shot down one of the planes. The pilot bailed out, but was dragged in front of Bradley. The normally taciturn general tore into the hapless pilot. "You stupid sonofabitch! Didn't you see our yellow recognition signals?" The pilot could only lamely reply, "Oh, is that what that was?" There are dozens of other examples of friendly fire from throughout the war.

Sources:

The Last Year of the Luftwaffe: May 1944 to May 1945 by Alfred Price

Luftwaffe Schlachtgruppen by John Weal