Cannot update iOS on iPhone 12 Max Pro.

The update bombs at random times. Also I cannot back up the iPhone (stuck with iOS 16)I have tons of space in the iCloud, far more space they needed on my iPhone itself. Update fails with message stating net work problems. I tried the update at four different locations and get the same results. from a friends home in Denver the back up fails with 1.04 GB remaining. In Santa Fe the backup fails much earlier. These 2 problems have been going on since June 2023. Note, I already spoke with Apple support and did phone network reset.m, did not help. Everything else working fine on the phone.