[curiouscats]

Is there an app that monitors your apps to see if any have been sold to such unethical companies to alert you to delete your accounts with those apps?

That would seem like a useful app.

Frankly Apple and Alphabet should offer such a service but I don't have much confidence that they will.

[mhh__]

This is actually really important for things like browser extensions.

[krembo]

Just use Little Rat to block unwanted call-homes, telemetry and stuff like that https://github.com/dnakov/little-rat

[test1235]

can apps see what other apps are installed?

[smachiz]

At least on iOS, only with MDM profiles for managed devices tagged as company owned I believe.