I had this problem with my iPhone 11 Pro Max with iOS 14 beta, back at the beginning of the year. I have no way of knowing if it was the beta software causing problems, but the eSIM would not work. AT&T could not get any eSIM to work, even with a new SIM. They removed the e-sim programming and it has continued to work with just the SIM all year. I got an iPhone 12 Pro Max in Feb and had no trouble with SIM/eSIM until this week, when on Tuesday, I went to zero cellular signal on both. I took it to an Apple store today and they ran diagnostics on it and said all hardware was fine, sent me to AT&T. They replaced SIM and eSIM, and could not get it to work. Back to Apple, and they said they couldn't troubleshoot it with beta software on it. I authorized them to factory reset and go back to 14.7.1, which they did, and when it rebooted, it would not set up the cellular service at all. They said that they can't do a repair if diagnostics doesn't register an error, but that they could clearly see something was wrong. Authorized the repair anyway, then said that the diagnostics system had flagged it as needing to be mailed in for repair. They gave me a loaner phone to use while it's being repaired. So here I am, two back to back phones with cellular service issues, both developing while running beta versions. Either it's an oversight in the beta software development that is really corrupting something, or it's poor implementation of the dual SIM that eventually craps out. Or we're all just extremely unlucky...