Will there be video evidence strongly implying that Joe Biden regrets dropping out of the presidential race, before the end of 2025?

Some things that would make this resolve YES:

Biden says he would have won had he been the nominee

Biden says it was a mistake to drop out

If nothing like this comes out, resolves NO at the end of 2025.

Things that wouldn't count (not direct enough):

Biden says top Democrats shouldn't have put pressure on him to drop out

Biden says he wasn't too old to run

I will not bet here.