Can I prevent tethering from using cell/mobile data? I have been using USB tethering to connect my laptop to a wifi and am scared I might lose connection to wifi and begin using mobile data without noticing

Ideally an app that lets me react to USB tethering being active and turns off mobile data would be great unless there is a setting that accomplishes this somewhere?

Thank you
If your mobile connection is properly deactivated, there is no chance to switch from Wifi to Mobile Data.

You can use the tiles in the status bar to do so (if you don't have it go to Settings > Status Bar > Tiles), or you can just go to the Settings menu and switch off Mobile Data from the main Settings panel.

If you want to switch automatically from Mobile to Wifi AND deactivate Mobile when you use Tethering, you can use apps such as Tasker to automate this.

If you have the "Developper" menu activated on the Settings, there is a option there that forces Mobile when Wifi is weak.
If the option is activated, just switch it off.