24 days ago - AndrewT - Direct link
Please try the following:

- unsubscribe from all mods in BOTH the Steam Workshop and the Paradox mod site mods.paradoxplaza.com
- delete the folder Documents/Paradox Interactive/Stellaris/mod/
- delete the file Documents/Paradox Interactive/Stellaris/mods_registry.json (if present)
- delete the file Documents/Paradox Interactive/Stellaris/launcher-v2.sqlite (if present)
- run the game up and check the launcher is okay with no mod or other errors
- subscribe to a few mods

- run the game up and see if those mods are now available to you.

I hope that does it for you!  
23 days ago - AndrewT - Direct link
What launcher version shows? Current is 2021.8.1

And what antivirus app do you use?  
22 days ago - AndrewT - Direct link
In the Windows search box enter Ransomware. Enable Controlled Folder Access if disabled, then go into the Apps Allowed through page there. Are any of our apps shown as having been blocked there? If so enable them ... steam.exe , stellaris.exe , and paradox launcher.exe should be in there too!