iPhone 11, Unable icloud backup
Turn off all things you can in iCloud settings. The idea is to back up as little as possible. Then turn them on half at a time till you discover which “group” is failing.
Or, contact Apple support. They can see the logs on the server side and tell what is messed up if needed. You will likely do some other troubleshooting like try a different network, but costumer support has the best tools to support your specific account.


https://support.apple.com/en-us/HT207428 ( what iCloud backs up )
https://support.apple.com/en-us/HT204247 ( reduce the size of your backup )