In JoJo Rabbit, Nazis attempt to mount a defense against an allied invasion even after Hitler's suicide was widely known. Is this accurate, and if so, why did they do it?

I loved Jo Jo Rabbit, but it should be appreciated as a caricature of life under Nazi rule, as well as the demise of the Third Reich, rather than a serious attempt to describe those events.

Hitler committed suicide on April 30th, 1945. It took about two weeks for German forces across the European theater to surrender. At the time of his death there were German forces fighting throughout Germany, but also hundreds of thousands of men still active in Austria, Italy, Denmark and parts of Central Europe.

Why did they fight even after Hitler died? I'm not trying to be flip when I say that it takes time for something as big as a world war to wind down. You're talking about something that has literally millions of participants locked in life or death struggle that had been going on for almost six years. Many likely didn't know about Hitler's death until a few days after it happened. Others were of course following orders from their own superiors, as for a few days at least it may not have been a foregone conclusion that Hitler's death automatically meant the war was over (although of course by then the result of the war was hardly in doubt and some individual commanders had entered into surrender negotiations even before Hitler's suicide). There was actually a succession after Hitler's death, as Goebbels and Admiral Donitz became the new leaders of Nazi Germany for just a couple weeks (with Goebbels of course committing suicide just days after his appointment).

Some of the will to fight on also undoubtedly was out of fear of what would happen to Germans if they surrendered. In the East in particular, the Soviet reprisals against the German civilian population were brutal and well known (as had been the German treatment of so many Soviet civilians), the Germans in those areas knew what awaited them which undoubtedly motivated some continued resistance, either out of fear or the hope that resistance in the East would mean more Germans could surrender to the Western Allies.

Related to this is that, among senior Reich officials in particular, the German actions of the last 6 years had practically created a death cult. By which I mean that the Nazis throughout WW II had crossed so many Rubicons that many who were involved knew that even if they survived the war, they may not survive the peace. The collapse of the Third Reich created a wave of mass suicides among Germans.

As for your side question, again, that scene in the movie is a caricature. That being said, things became very desperate towards the end of WW II, with relatively young children and old men conscripted into the ranks and sent to fight with very little training, sometimes issued with just a Panzerfaust in the hopes they could knock out an enemy armored vehicle.

There are a ton of books about the fall of the Third Reich. The Third Reich at War by Evans is a good one. The End and Hitler: A Biography, by Kershaw, are two other good sources.