Which versions will work with newest release and which ones must I make new

I have a few worlds in versions 1.12.x and 1.16.x and 1.19.x

If I play by starting 1.20.1 in the launcher, will those worlds become 1.20.1 or will they be corrupted and lost?

Compatibility warnings or notices would be very handy.
I've already opened my 1.19.4 as 1.20.1 and it let me play and now it reads 1.20.1 in the world list, but did it really become that or does it need complete world regen from scratch by using the same world seed to be properly 1.20.1?