No IMS Registration, VoLTE, VoWiFi on Lake. LOS 18.1

Expected Behavior

Activation of corresponding options in settings should enable VoLTE and VoWiFi. T-Mobile US prepaid.

This is effectively the same issue as #3371 (closed) but with Lake rather than Ocean. Also see #3269 (closed)

Current Behavior

I'm having issues getting volte to work on a XT1965-T (Revvrly+ branded G7 plus, T-Mobile US) phone. All the options to enable it are there and I've tried all the obvious solutions like disabling/re-enabling the volte and radio settings, resetting APN settings, etc.

LTE works fine otherwise and I can make calls though having it drop to 3g is annoying particularly when there is no 3g coverage preventing me from making a call. It would also be very nice to have wifi calling.

Steps to Reproduce

When dialing *#*#4636#*#* then choosing "Phone Information" then choosing "IMS Service Status" from the drop down menu in the upper right, it reports:

    IMS Registration: Not Registered
    Voice over LTE: Unavailable
    Voice over WiFi: Unavailable
    Video Calling: Unavailable
    UT Interface: Unavailable 

/device lake /version lineage-18.1 /date 2021-05-11 /kernel 4.4.250 /baseband M636_21.71.02.66R /mods no google apps, stock lineageos 18.1

I have read the directions.