This one worked for me (VoLTE and WiFi calling) in Poland on T-Mobile (heyah 01).This module works for me for VoLTE. 5G is not working but I'm not sure if it's caused by network coverage in my neighborhood.
GitHub - swangjang/Pixel-Redbull-Carrier-Patch: This is a Magisk module (in testing) for Pixel 4a (5G) and Pixel 5 that enables 5G for Unlisted Countries, VoLTE switches in the settings and add support for more countries/carriers.
This is a Magisk module (in testing) for Pixel...github.com