Drupal 9 → 10 Upgrade paths

Replacing Stable with Stable9

This update includes support for Drupal 10; historically Prototype relied on the Stable theme, this has been updated to Stable 9 and includes a post update hook to support this change. Your version of drush impacts if using the provided update file will run, see below for specifics.

drush 11 vs drush 10

When running drush updb, please make sure you are running drush 11 otherwise you are likely to run into errors.
Run updates via drupal interface if using drush 10 or less.
If errors already appeared, use either drush theme:uninstall classy stable
and/or drush theme:enable stable9 depending on which php errors you received.

config

If using configuration synchronisation, make sure your core.extension.yml contains

theme:
...
stable9: 0

instead of
theme:
...
stable: 0
classy: 0