In my experience 80% packet loss makes most common protocols basically unusable. Yes you can still get data out...but many apps will just fail due to timeouts and other things.
Matrix published a proof of concept a few years ago of an alternative transport layer designed to work over connections with a few hundred bits per second, and massive packet loss, while still providing E2EE:
https://matrix.org/blog/2019/03/12/breaking-the-100bps-barri...
I imagine the people with illegal starlink terminals are fairly tech savy and can use custom protocols. Living in Iran they probably already have a lot of experience with vpns and lower level protocols to evade censorship.