Actually Android updates have not been satisfactory for many people. I had initially Android 10 that updated to 11. All kind of problems started happening (including battery drain and band allocation). So I went back to Android 10 and things were back to normal. When Android 12 rolled in, I tried it and found it to be better than 11 but still buggy. So I am again on Android 10 and staying here.
I am glad to learn that your phone was working well on Android 11. In terms of your ringer not working, here are possible scenarios:
1. Please check if your phone is in do not disturb mode.
2. See if your ringer‘s volume is mute.
3. If you change the ring tone, does the phone ring to give you a sample?
4. Have you installed any modded application (like Dolby Atmos, DTS etc.) that do interfere with ringer many times.
5. Please try these ringtones that are here
. See if these work.
6. I am going do some research to find a solution.
As for the firmware, if you look at the list the T-Mobile ones are labeled TMO in the first column.
The firmwares are originally written by LG but given to various carriers who customize it to their phones and operating bands. So Mint Mobile operates on a pre-allocated band by T-Mobile. Now T-Mobile does not put its direct subscribers on those bands/frequencies. Hence the T-Mobile firmware does not include the Mint mobile bands or frequencies.
If you do flash a T-Mobile firmware, for example, your phone will be fine but the modem may not operate as it will be looking for T-Mobil network bands not Mint mobile. That’s the arrangement that MVNOs have with their carrier partners to protect each other from customer defection. In other words, if you go to the carrier directly you get better service and option albeit higher price. And if you go to MVNO, price is lower but you sacrifice service options.