[Upgrading, Modifying and Unlocking] seawildflower:
EDIT: The great and powerful @nuttydoc simplified this greatly. See post #259. Ill leave this up in case people still run into problems.

Okay, so this is what I did.

I was not receiving calls. I could make them and had great quality, but could not receive. This could be caused by a few things.

1. Sim card was not installed during initial setup. This mattered for me. For whatever reason some of my sim settings were locked and was unable to make changes. factory reset is the fix for this. varying degrees of functionality may occur, including not being able to receive calls.

2. Pixel IMS was Installed. Pixel IMS worked for android 11 but does not work properly on LOS20. It also doesn't play nice with Treble IMS app included in Phh's Treble Settings. I found that when I went to sim settings page nothing would load and/or settings app would crash. I could make calls but could not receive them. sms worked fine.

MY SOLUTION

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IMS initialization is very finicky. If your having issues I recommended starting with a factory reset. Lineage has a backup solution built in, I have not tried it but it looks like it does work. check system settings to find it.

1. MAKE SURE SIM IS INSERTED BEFORE FACTORY RESET

2. do a factory reset through android system settings.

3. set up device. connect to wifi during setup.

4. go to Phh's Treble Settings, Go to IMS features.

Install IMS APK for Qualcomm,

press create IMS APN

(I rebooted here, may or may not be needed)

check request IMS network

select force presence of 4g Calling settings

5. go to Misc Features in Phh's Treble Settings

scroll down to telephony near the bottom and select "Allow binder threads on incoming calls"

reboot

6. Go to Network and Internet Settings

Go into SIMs

select VoLTE if it is not already selected. If you dont see it something went wrong. double check that you selected "force 4g settings" in Treble IMS settings.

set "preferred network type" to LTE

Test calling, sms, send and recieve.

You may find that you have LTE for a little bit, then you will lose it, this happened to me. though my call quality was fine. you may try to request IMS again in treble settings by pressing "create IMS APN'. Its hard to tell if anything happens as nothing visual occurs when you select it. Possibly another reboot could be helpful. I went from having LTE, 3G during calls (Though quality was perfect) to H+, while having a data connection, then all of a sudden, LTE appeared and has been working flawlessly ever since even after multiple reboots, rooting, etc. To me this tells me some fetching happened from my carrier and it took some time to complete. This is a complete and wild guess. so if you go back and repress "create IMS APN", maybe give it some time, make some calls, whisper sweetly into the microphone, encouraging the phone, telling it it's just as good as all the other phones. You can also try to reset network settings in system before a factory reset, I recommend trying, but It did not work for me. Especially when I had Pixel IMS installed.

To me, the problem lies with IMS settings being very picky, needing to be setup before anything else, on a fresh install, with SIM installed, with a slight wind blowing to the east, I also sacrificed a chicken just to be safe.