And this has to do with Workshop and mods how exactly?

And if you switch to offline play you won't get updates until you decide to go back online.

Also Turn off Steam Cloud for Titan Quest Anniversary Edition, it is bugged and creates issues.

General Steps
Please follow these steps and try in-between in this order
- Restart Steam and be online.
- Run TQ.exe in admin mode.
- Verify files
- In case of the game not starting / crashing on startup:
* Exclude the game's installation directory from your antivirus program's protection mechanisms
* If on Windows 10: Disable the ransomware protection of your documents folder (system settings --> ransomware protection)
- Restart computer
- Update Graphic Cards (GPU) drivers
- Update Windows
- Reinstall the game and delete all folders and files related to TQ. (make backups of your save files first).
- Reinstall Microsoft .NET Framework (see guide on internet)
- Reinstall Visual C++ Redistributable (see guide on internet)
- Report it here: https://redmine.thqnordic.com/projects/titan-quest-eternal-embers-community/issues/new
Please provide as much information as you can. Screenshots or videos is possible.