At the current moment, squaremap doesn't have some tags populated, which makes it incompatible with packwiz.

Example with other mod (note the "Server" label next to it)

As for now, this causes that mod to not be installable via packwiz modrinth install command, and also hurts discovery of the mod at least a tiny bit (especially when filtering for server-side mods only)

Also a tiny question: on one of screenshots it shows "terralith overworld" which is separate from the main one. How did you manage to do that? I'm gonna try doing it with multiworld but I just wanna know what you did here

I don't see an option to set that anywhere:

I'm not opposed to configuring this if possible, but it seems like an issue with the package manager if it doesn't consider unspecified the same as client & server.

Huh, and nothing in general/description? I've never published anything on MR myself, so I'm not sure..

You are not able to change if your mod is Server-sided or Client-sided after creating the mod. You'll have to email modrinth to get it fixed.