Why didn’t they put it on F-Droid? And does Proton mail support connecting via SMTP or POP from third party clients, like every other mail service does, yet?
Very good - unless Proton Mail is their first email account. Forcing (or strongly encouraging) them to have a Google account first is counterproductive.
You can install Canta from F-Droid that allows you to easily uninstall apps with just one device, and gives you a short description of what it does. https://f-droid.org/packages/org.samo_lego.canta/
I’d have to ask people to install a new app and set up an account, but they all already have Google account
If you’re not willing to take that minor trouble, no one will be able to help you. Sounds like an excuse to use Google rather than an actual good reason.
It would ironically probably make the app blocker harder to get past if it is open source, so it would be more effective than these commercial solutions.
Still don’t let you boot other OSs, or sideload apps, or use third party browser engines outside the EU, or use third party SMS or phone apps.