If the goal is to prevent telemetry, you could use Little Snitch to blacklist all Logitech applications from being able to go online.

Yep that would work.

I do sometimes wish there was a built-in save sync feature though.

I’ve needed to help a few clients with this problem. Google recently started enforcing oAuth 2.0 for their accounts. I could be wrong, but I remember reading that OS X Sierra and High Sierra don’t support oAuth 2.0, so you can’t use Apple Mail unfortunately without upgrading.

Have you considered using an alternative?

Edit: I stand corrected. App Passwords are a thing.

The only caveat with the Logitech Combo Touch is that it’s noticeably a lot more heavy in comparison to other cases. It offers good protection however. If I were buying another case, I’d be hesitant to get it again.