@Ivi @SubCee @iode-1520 in all of your cases then, you had working VoLTE calls with v7.4 (or v6.x if on that previously) but upgrading to v7.5 then broke VoLTE (for Sunrise carrier only)? Since Ivi notes the issues with a Pixel 7a and P7P with Sunrise and not with Swisscom I still wonder if there is some level of APN config that is at play here. IPV4/6 issue? Maybe even Sunrise’s customer support isn’t in sync with recent changes from their tech / network side?
Broader searches for related issues (/e/ forums or LineageOS reddit, etc) would probably be the next place to go. I did a super quick search, you guys will need to do more to dig in deeper, but I see these pop up right away on the /e/ forum, for example, without any solution: