The script intentionally reverts the Docker repo to the bookworm suite in case of ARMv6, which works well, as far as I tested.
Generally: you only ever need to manually revert trixie to bookworm when using 3rd party repos which do not have a trixie suite yet. But you should never need to manually change them from bookworm to trixie. If the script reverts it, then because the trixie suite does not exist yet, and hence you would run into the issue you do now run into 
. I do somewhat regularly check back the status, and once the trixie suite does become available for those known cases, the respective next DietPi update will perform that switch automatically.
EDIT: Ah, sorry, the upgrade script checks for the wrong list name dietpi-docker.list instead of docker.list, as we did not apply the convention there. I’ll fix that just now. So the correct fix right now is:
sed --follow-symlinks -i 's/trixie/bookworm/g' /etc/apt/sources.list.d/docker.list
Fixed with: dietpi-trixie-upgrade: fix Docker APT list name · MichaIng/DietPi@b897f3b · GitHub