When I change any settings (Conditions on when to show Hunger Bar, Health Bar) and restart the game, the settings are restored to default.
Also I do not find any config-/ json file to make the changes persistent.

What can I do to fix this?

That is odd behaviour that I cannot replicate. Running the mod should create a file config/autohud.json5.

What version of autohud & clothconfig are you using (I tested with autohud 2.1 and clothconfig 7.0.72 & 7.0.73)? Is your config folder writable/do other mods keep their settings?

Thanks for the quick reply.

I use cloth-config-7.0.72 and cloth-api-4.0.65.
other mods save their settings (at least from which I tested until now).
the config-file is not there which might be the problem..
Permissions are correct (rwx) (I'm on Linux)

I found out what causes the issue.
I used to have the /config directory symlinked from a central folder (for subversions eg. 1.18 / 1.18.2)
I'm using MultiMC and the /config -folder is within the multimc directory:

Source: /multimc/mc_config
Symlink: /multimc/instances/1.19/.minecraft/config

Somehow some mods cannot write into that symlink, where others can.

Another mod that can't is "DynamicCrosshair"..
Just to let you know, maybe it is fixable (to write into symlinks aswell).

But as for this issue, it can be closed. :)

Oh, interesting. I'm using clothconfig's AutoConfig for both mods, so I assume that all mods using that would have the same problem (but I don't know which do!)... maybe I'll work on migrating away from autoconfig. Thank you for the information, and I'm glad you solved your problem!