I get the following error on upgrading to 4.0. I'm trying upgrade a 9.5.10 site to Drupal 10 and 4.0 is required to make that happen.
Twig\Error\LoaderError: Template "modules/contrib/views_fieldsets/views-fieldsets-div.html.twig" is not defined. in Twig\Loader\ChainLoader->getCacheKey() (line 45 of /[site]/web/core/themes/stable9/templates/views/views-view-fields.html.twig).
Yes, I see it's looking in stable9, which is deprecated - I've been going through the wars on this at https://www.drupal.org/project/drupal/issues/3328016 🐛 Deprecated core themes cannot be disabled on the "Appearance" tab because they are hidden Needs work
Any suggestions greatly appreciated!
Closed: outdated
4.0
Miscellaneous
So stable9 isn't deprecated but stable was and removed in D10.
the 4.0.x branch things were moved to a traditional folder, should of been found with a cache clear.
Wonder after a cache clear if that resolved your issue?