18 days ago - Shurenai - Direct link
Generally, you can move from Minor versions (A20.1->A20.2) with no problems. But moving from Major version to Major version (A20.x->A21.x) isn't possible, the game prevents you from loading the save because the differences between versions is too big, and most likely result of loading it would be corruption.

There's some sort-of workarounds people in the community have come up with, but, for the most part, Even the workarounds have a big host of problems that often make it more trouble than it's worth.