I understand your frustration, but software fixes take time. Especially if manpower is limited - as you may have noticed, most bugs are unassigned. The issue is likely as simple as not having had the time to verify that this bug is real.
What makes this extra-tricky is that it is not immediately obvious why some apps have this problem and others don’t, so finding the source of the problem can be a pain.
Also, I’d suggest submitting this bug to the maintainers of Linphone too, but while Linphone is supposedly open source, it’s not on Github. So on top of the similar low-manpower problem, they don’t use a modern bug tracker but a GNU mailing list (the project started in 2001, so it makes historical sense, but this is still very frustrating)
In the mean time, have you tried going into settings and tweaking the video presets to see if it has any effect? I can’t test it myself right now because it requires that I actually call someone before I test the camera (bit annoying; in general not a big fan of the interface, to be honest). The only contact I have is in do-not-disturb working mode.
Alternatively, according to [its wiki page](https://en.wikipedia.org/wiki/Ring_(software)), Ring seems to support SIP, perhaps it works as a replacement client:
Find it on F-Droid by typing “cx ring”
Adding an SIP account is a bit hidden away, you have to tap the triangle next to your own:
I uh… haven’t managed to successfully move over the settings from linphone yet, if you succeed let me know. So I also can’t comment on whether the video calls actually work, sorry.
(also, last time I tried Ring, it drained my batteries like crazy. However, that was an earlier beta so hopefully things are better now. And you can turn off Ring account, in which case it shouldn’t be wasting battery connecting to the decentralised Ring network)