emacs-undo-fu VS emacs-undo-fu-session

Try undo-fu, it's a thin wrapper on emacs built-in undo/redo but doesn't have this limitation.

Try undo-fu it was written to address exactly this problem.

Emacs has a good built-in undo function. And that one can be beefed up further with undo-tree --- which I used for some years --- or undo-fo --- which I use now ---.

I switched back from undo-tree to undo-fu, which re-uses the emacs undo-system instead of replacing it and makes it more intuitive to use while still preserving the full undo history. I sometimes miss the nice visualizations such as the tree and I didn't even know (or remember) the diff, but in 99% of cases I just need simple undo and most of the time I have git anyway to save intermediate states of my files.

There are packages that were written to add an explicit redo command, such as Undo Fu (https://gitlab.com/ideasman42/emacs-undo-fu) and Undo Tree (https://www.dr-qubit.org/undo-tree.html). Again, these packages are not needed in Emacs 28. That variable you found tells Evil which feature/package you want to use for an explicit redo command.

Had so many problems with this (once a month/week) and lost work... that I gave up and wrote undo-fu and undo-fu-session.

Did you try undo-fu?

undo-fu-session can be used for persistent undo with emacs built-in undo.

undo-fu-session persist buffer undo between Emacs sessions

If you want auto-saved undo history undo-fu-session, a separate project, it doesn't depend on undo-fu but is compatible.

Had so many problems with this (once a month/week) and lost work... that I gave up and wrote undo-fu and undo-fu-session.