Same here. Tried to unsubscribe mods several times, but didn't work at all. It says "This archive path in this mod's descriptor file is invalid or does not exist", and I checked the steam workshop file, they were all in the generic workshop mods place. Don't know why it works this way. Frustrated.
Edit: I have tried to subscribe to a CK3 mod, and it worked just fine. Also I tried to create a new mod using the "mod tools" in the launcher, yet it didn't show up in the launcher mod list. However, it was created in the Victoria 3 mod folder. Fascinating.
Edit 2: Reinstalled the whole game and problem solved.