I simply used the internal updater to update ROM and recovery and everything went fine. No data loss.
For backups I'd recommend rooting the device with Magisk. Any other non-root backup method seems not really so much better than the standard Google Drive backup IMHO.
There's SeedVault build into LineageOS. That backup solution served me admirably, and you can even upload it to NextCloud, where it can be automatically downloaded on restore.