In the move from Lineage 22.x (iodéOS 6.x) to Lineage 23.x (iodéOS 7.x) there have been instances of APN settings getting a bit mangled. I have tried to follow the LineageOS development in that regard, but it is a bit confusing why the regression (they do generate their default APN settings differently now, but it seems like the output should be the same?). Anyway, I suspect that is what happened for you.
I did try to help someone with Sunrise CH in the past few months, I can’t recall if they solved it or not. The best I can find for manual setup on their site is for a Moto device: Instructions for your mobile phone | Support which seems fairly basic, just use “internet” in the APN field, and ipv4 only.
You can check the VoLTE registration by using *#*#4636#*#* and then going to “Phone Information > 3 Dots > IMS Status”