Found that if I went into the apps store with all my apps .update the Amazon prime app then it actually came on for the first time . I'd get the whites dots for ages then it would just go off .
I tried signing in and out of my Amazon Account. That didn't work. I uninstalled the app and reinstalled it. that didn't work. I unplugged my TV for one minute, then plugged it back in and pressed the power button on the Samsung remote and held it for 30 seconds and that did work for me.
I have the same problem with my Samsung Q9FN TV. The Prime Video freezes everytime whenever I access Prime Video and click on any title. The only way to get around this problem is to do a cold-boot of my TV each time. With all the other apps (i.e Netflix and others) I'm using Prime Video is the only one that I have problem with (freezing). What I have noticed was that the problem does get resolved by itself eventually if I left it on frozen for 10 mins and miraculously it gets unfrozen. I think the problem is with the Prime Video server hanging or it's waiting for something. I believe the Prime Video app or TV is not the culprit since it does get resolved by itself eventually if I waited long enough.
Sounds very similar to the issue I'm having on my 2019 frame. I have for the moment given up on using the prime-app and cast from my iPad instead. It's a bit annoying, hope there is some kind of fix coming soon.