How to backup iPhone 8?

Instructions state to be sure your screen is locked. How can I start a backup with the screen locked? The instruction seems contradictory. In any event, the phone shows the last successful back up was in May 2022. When I select 'Backup Now' it tries to do so but quits. I have lots of room in iCloud. So, that should not be a problem.

I tried contacting Apple Support. They suggested I needed to download the latest IOS version. I did so. But it didn't make any difference. Don't know what to do next. Any suggestions/help would be appreciated.

Yes, I've read the Apple instructions but to no avail.