you have created version 1.21, but is version 1.20.6 compatible with version 1.21?

The version for 1.20.6 won't run on 1.21, it just wasn't made for it.

The version for 1.20.6 won't run on 1.21, it just wasn't made for it.

In that case, why create version 1.21 before version 1.20.6? It makes no sense.

In that case, why create version 1.21 before version 1.20.6? It makes no sense.
Because more people want it.

The version for 1.20.6 won't run on 1.21, it just wasn't made for it.

In that case, why create version 1.21 before version 1.20.6? It makes no sense.

1.21 was released 1 month after 1.20.6 so a lot of mods did not brother with updating to 1.20.6 and just skipped it

But looks this mod with version 1.20.4 cannot working on 1.20.6? Because my server is crashed when try to load it.

Sorry, my mods don't support 1.20.6 and we're not planning on porting to it due to time constraints.