Warning: 'Undefined array key' on page 'Manage form display' when changing field settings.

Above patch does not sovle anything, just adds the annotation description, reorder functions and updates // @todo comments

It is assumed that the problem is caused by 🐛 Multiple Office Hours fields on same Content Type breaks Exceptions Fixed .
But this is not confirmed, and the version 8.x-1.11 must be tested, to see if already happens there.

I cannot reproduce it anymore.

This issue has reappeared on Drupal 10.x.
It occurs when clicking the settings icon in "Manage Form Display" when all of the following conditions are satisfied:
1. The office hours field is used in a paragraph
2. There are other fields in the same paragraph (e.g. a Text (Plain) field)
3. Widget type is either "Office hours (week) with exceptions and seasons" or "Office hours (week)"

NOTE:
If office hours field is the only field used in the paragraph then there is no issue.
Add a second field to the paragraph and the issue will show.

Patch: https://git.drupalcode.org/project/office_hours/-/merge_requests/46.patch

Hi

Im using Drupal Core version 10.1.8 but I can't seem to replicate the error.

The patch effectively removes all initial settings in the 'settingsform'. That seems a bit rude and tricky.
OTOH I cannot find a new problem.