Just as a reference, here’s what you could do with an unlocked bootloader (a procedure needing some sensible thought about security implications beforehand, and which forces a factory reset, and which Apps relying on Google SafetyNet compliance like e.g. many banking Apps might not like afterwards):
Backup …
- Boot TWRP … making sure the system partition gets mounted read-only to not break OTA updates of the OS.
- Use TWRP’s Backup feature while being aware that TWRP doesn’t backup Internal Storage.
- Copy Internal Storage to a computer via USB (you can do that when TWRP is booted) … and/or boot Android and use something like MyPhoneExplorer to sync anything you like from the phone to a computer.
Restore …
- Boot TWRP.
- Use TWRP’s Restore feature to restore your backup.
- Copy Internal Storage back to the phone via USB (you can do that when TWRP is booted)… and/or boot Android and sync your stuff back using something like MyPhoneExplorer.