Make sure your cell phone provider connects to the same network bands as what the phone supports. This is important because every carrier may support 3g/4g/LTE but connect with different bands. You have to do some research on your end and when you do find the right carrier, the phone will not have these issues unless it is defective device itself.
Not using SFOS myself since many years. But others indeed have reported much better results. As you had similarly devastating experience with Droidian, also (kind of) positively tested by others, I wonder if something is wrong with your device. Did it work correctly with stock Android 11?