Does biome generation change after 1.16? I mean not in how each individual biome looks but as in where each biome gets placed? In other words, would https://www.chunkbase.com/apps/biome-finder give different output for 1.16 and 1.17/1.18?
If yes, what happens to worlds generated in 1.16? Is there then a mismatch between already generated chunks and the biome displayed in the F3 overlay? -> wrong grass colors, mod spawns etc?
I'm not 100% certain about 1.17, but from what I've read about 1.18, definitely biome placement is changing in each snapshot.
I assume you meant 1.16 in your second paragraph rather than 1.6? Either way, try it! Generate a world in 1.16, then open it in a higher version. This is trivial to do with a launcher like MultiMC, but I'm sure it can be done with the vanilla launcher as well.