Symfony\Component\Validator\Exception\LogicException: The LangcodeRequiredIfTranslatableValues constraint can only operate on the root object being validated

I can confirm I'm having this error twice now (on two different sites), and it doesn't allow me to change any text format configuration that has CKEditor5 anymore.

Drupal 10.2.6 doesn't have this. This doesn't come out of the box but after playing around with CKEditor toolbar or removing a text format.

Confirmed, I have the same problem after updating to Drupal 10.3.0-beta1
Exactly the same errors mentioned above.

I updated to Drupal 10.3.0 and the problem still persists which is very irritating.
Is there a chance for a quick solution so that I can edit the text format settings?

Yes. Performing a git bisect on a checkout of Drupal Core between a good and bad release tag will quickly find the issue that introduced the regression.