Because most of vanilla mods does not works with WotC and vice versa, so always search the right mod for your game.

Well on the steam tab it says I have XCOM2. But I also have the WOTC DLC. So does that mean I should ONLY take mods from the WOTC page? Even though the name and banner image is identical to the one from the XCOM2 mods page?

If you play WotC add WotC mods only, or if the mod states that it works both version then you can add it too.

Steam Workshop for XCOM2 has both base game and WOTC mods, you have to pay attention to the tagging to make sure you get ones for the version of the game you are playing. Just "owning" WOTC is not enough to use those mods, you have to be playing it. WOTC is not a typical DLC that adds one thing or one mission or a tiny bit of extra story, it adds content to all parts of the game, from beginning to end. More of an expansion than just a DLC.

As a consequence the WOTC game files are almost completely separate from the original game. Therefore mods made for WOTC won't work for the base game and vice versa (mostly).

If I may suggest, search "github alternative mod launcher" and go grab the XCOM 2 and Chimera Squad open source third party launcher. The column to the right states which game a mod is for as well as cross references dependabilities automatically.