It should become available in the launcher for you to enable/disable. Find some mods that you want to use and simply Subscribe to a mod you’d like downloaded. Open STEAM, go to Library, click on Crusader Kings 3 and go to Workshop.

The staff scan all mods before they upload, so don’t worry and mod away! How do I install CK2 mods? I been using it for the last several years and never (to my knowledge) ever got a virus or malware of sorts from a Mod.