I'm using the Distant Horizons mod, which pushes the vanilla fog much farther from the camera, up to the ends of the LODs.
However, BCLib overrides fog handling, which is why I have to completely disable these settings:

However, there is no config file in the config/bclib folder. It's always an empty folder.
Therefore, after re-entering the game, the near fog appears again, forcing you to manually turn it off each time via Mod Menu.

Showcase of a problem in a new world:

BCLib 21.0.5
Fabric API 0.100.4+1.21
Fabric Loader 0.15.11
Minecraft 1.21

Here are the logs.
It doesn't really matter what other mods are installed.

I can generally assume that this is a Cloth Config issue, but I'm still not sure, since other config files are edited and saved normally.

Happens for me too

me too

Should be fixed with the latest version.