"Wouldn't the liberation of Prague by the US basically guarantee that Czechia would be in the western bloc?"

Not really. The Western Allies and Soviets generally had already agreed-upon zones of occupation regardless of where actual military forces ended up on V-E Day. In the case of Germany, a substantial portion of what would be the Soviet occupation zone (and the future German Democratic Republic) was west of the Elbe, which was the agreed meeting point of Western and Allied forces at the end of the war. These areas were vacated by the US military and turned over to the Soviets. Similarly, the Soviets were in possession of all of Berlin on May 9, 1945, and turned over the agreed occupation sectors to the British, French and Americans after hostilities.

Czechoslovakia is a little different since it wasn't an occupied enemy country, but a liberated Allied country with a government-in-exile that had relations and agreements with both the Soviets and Western Allies. All Allied military forces vacated the country by December 1945. From this point the country essentially had a democratic government with free multiparty elections, with the Communist Party being the largest party and recipient of votes (but not a majority). It participated in government and the Soviets hoped a fully-Communist government would take power democratically. This didn't happen, and the constitutional crisis that ultimately saw a Communist-only government gain power in 1948 is described further in an answer I wrote here.

You'll occasionally see a "what if" alternate history usually revolving around the fact that Patton's 3rd Army was already in Czechoslovakia, as the Americans by agreement with the Soviets were allowed to advance up to Plzen. On the night of May 7 twelve US armored cars advanced from there to Prague: it was a scouting party. The Soviet forces (mostly the 1st and 2nd Ukrainian Fronts) insisted that they were planning to take Prague, had operations underway, and that US forces should remain at the demarcation line to avoid friendly fire. Soviet operations lasted from May 5 to 11 (after V-E Day) and were concurrent with an uprising in Prague by Czech resistance against the Germans.

Claims are made that parallel similar claims/criticisms against Eisenhower and the possible taking of Berlin: he shouldn't have been so nice to the Soviets, taken what he had the opportunity to, and that this would have significantly altered the future Cold War borders between East and West. These speculative claims and criticisms I think are made with far too much hindsight: no one was really planning for where exactly the post 1947/1948 "Iron Curtain" would be, and the immediate concern was where to stop to avoid unnecessary clashes between Soviet and Western forces. Why take something in a way that would needlessly antagonize the Soviets while the war was still on, and that by existing agreements would be evacuated anyway?