You’re very kind to your phone! I might have to try that if I can’t identify an app (or apps) that is causing my battery to drain so fast.
Thanks for your patient advice! This didn’t make any difference, but I did manage to fix the problem. I deleted my original install of adb (which was v1.3 from here: https://forum.xda-developers.com/showthread.php?t=2588979) and instead installed the ZIP file from here: https://www.xda-developers.com/install-adb-windows-macos-linux/. When I ran a PowerShell prompt (which seems to work as well as command prompt), it first gave me an error message, saying it didn’t recognise adb - but it prompted me to use “.\adb” instead. That worked fine, and then my phone did prompt me to accept USB debugging from my computer.
Thanks for all your help!