Thanks to the DietPi staff for the effective upgrade script for Bookworm!
I recently upgraded from Debian Bullseye to Bookworm on an HP mini PC (Native PC x86_64) using the DietPi upgrade script.
I had no errors or issues with the upgrade via the console. As expected, I did have trouble with a Nextcloud 25.X upgrade not supporting PHP 8.2, as it would not run after the incremental upgrade. I recall an error message on the Nextcloud web page that my current version doesn’t support PHP 8.2. (Perhaps an issue with the PHP version check patch.)
The solution was to reinstall Nextcloud using “dietpi software-reinstall.”
Then I could finish the incremental upgrade to 25.0.13 and then upgraded to 26 via the admin GUI.