Anyone still experiencing this issue using D10.2+ and content moderation should note that the latest patch in #94 will fail as the code is already added to Core.
We experienced the effects of the current issue after having added a boolean field to all content types, which all have translations enabled. We could not save a new translation without manually saving the base node first.
The patch in https://www.drupal.org/project/drupal/issues/2955321 🐛 Unable to change non-translatable field value on translatable content with content moderation enabled Needs work (#77) fixes the issue for us.
Re-rolling patch from #30 for 2.0.x branch. (There is no option to test with that branch though. Tested locally and patch applies.)
Re-rolled the patch in #14 to improve the language used in comments and the UI. The functionality works great in the original patch.