What can I do to see the intetnet traffic from individual apps
what I might want to block?
One strategy is to block everything, and open ports as needed. Beware that most guides focus on inbound traffic, whereas you seem to be focusing on outbound traffic.
That’s odd… all the projects i use document their install process fairly well, most of them using either cmake or autotools.
The only “terrible” scenarios i occasionally encounter is, yes, trying to automate the android toolchain - i blame Google though, not C/C++ as the Android toolchain is intentionally designed to be used with Android Studio and trying to veer of that is increasingly harder.
Even cross-compiling for windows isn’t that bad.