@thebroison Unfortunately, there are no devs working on this. Sounds like a new port for 3a/3aXL might be needed / the easiest option? The guy who was maintaining the Pixel 3a, who has done a LOT for UT, can't test on his own carrier due to no VoLTE support, didn't get the help he needed, and has moved on.
While we all like to see older devices maintained, my impression is that with the amount of challenge required, it might be better placed into newer devices at this point.
This said, there are certainly others who'd like to make VoLTE work on the Pixel 3a, and if people pull it off, that's fantastic. But like all these community efforts, it'll be down to you and the others involved to make it happen.
You'll find that there are other posts on this topic on the forum, and in the Telegram UT North American Carriers Issues channel, so if you want to try to help, you may not be alone!