Is it possible to destroy every single block on minecraft?

I heard it is possible and wanted to try it. I'll be using lots of TNT, and of course it'll take a long time. I'm going to save and it and work on it just like you'd do if you're in the process of building something over the course of days.

if not in the overworld, how about The End, since that is pretty small compared to the overworld

Yes but it will take an insane amount of time

The overworld endless spawns so it isn't possible. I believe The End has set dimension so it may be possible but I'm not sure.