Speaking of VoLTE - For your information only!
An excellent unofficial LineageOS 23.2 (27.05.2026) build by @krazey90 is now available for the Samsung Galaxy S9 (starlte) / S9+ (star2lte) / Note9 (crownlte), featuring working VoLTE + VoWiFi including OTA update support. I also use the MicroGPlus add-on by @TheHitMan since there’s no alternative for me. For more information, check out XDAforums.