Yes, you can use their exact build environment straight from GitHub. You can also use Molly.im which is another app that i think is a fork? Im still investigating it.

That’s kind of a core tenet of libre/open software, innit? Independently verifiable software that you can change at your pleasure.

I was looking at Molly.im and it has its own f-droid repo. There are two options: with and without Google servicios.