Tried more solutions I found here, eventually lost every single world, server IP, mod etc I had.
In conclusion: if you get this error, don’t bother fixing it, unless you are ok with losing literally everything you have done so far in minecraft.
Got this on 1.12.2 today for the first time, and after that it happens in every other version as well. Reinstalled minecraft completely (backed up worlds and deleted all the other files) two times, but the issue is still there.
Theo V
Tried more solutions I found here, eventually lost every single world, server IP, mod etc I had.
In conclusion: if you get this error, don’t bother fixing it, unless you are ok with losing literally everything you have done so far in minecraft.