same wont even fully launch

Another way to do it is to go into Valheim directory and locate the BepInEx folder. rename that folder and start the game.

Thanks for pointers. Valheim started after the PC reboot.

From Valheim Plus FAQ

How do I disable Valheim Plus?

To disable Valheim Plus, you can do the following:
1. Open the doorstop_config.ini in the root of the Valheim game's folder. i.e. 'C:\Program Files (x86)\Steam\steamapps\common\Valheim'
2. Change line 3 from 'enabled=true' to 'enabled=false'
3. Save the file, Valheim Plus should now be disabled when you launch the game.

same

Same here. Waits for about a minute while showing Valheim logo. Then exists.