I have tried many other mods and they all work in my modpack, but only the alexmobs mod does not work, the exit code is 1.

Is there any solution?

This code might mean that you're missing a required mod. Did you get Citadel? There is a link at the top of AlexsMobs page.

Having the same issue with this specific mod, also made sure i had citadel installed. could it be a corrupted config file? is so then how to fix?

Looks like the problem I had is gone, can't reproduce it anymore.

Well wanted to test the mod and got the same error and found out why , but don't know if It's the same problem.

Looks like curseforge ( I think) is doing something wrong with adding citadel:

As you see it's the same file size and the same md5 hash, somehow the mod citadel is the same mod file like alex mobs's...

Workaround:
Download citadel from here for version 1.20.1 and overwrite the citadel file in the mods folder:
https://www.curseforge.com/minecraft/mc-mods/citadel/files?page=1&pageSize=20

To get to the mods folder: Right-click the profile -> "Open Folder -> mods.

I searched around, but found no option to clear a cache in curseforge or where curseforge is caching downloaded mods.
Maybe a reinstall could fix that problem, but I don't want to do it...

ya I'm getting this problem too with this mod when i try to open a new pack that I'm working on.