Fields can declare column_groups to allow setting some of their properties as translatable.
This has no usage in Core for now but might be happening with
✨
Allow to configure translation per property on link fields (for translating only the title, not the url itself)
Postponed: needs info
someday.
When using this kind of field on a new translation, \Drupal\content_translation\FieldTranslationSynchronizer::synchronizeFields(), called by content_translation_entity_presave(), throws an exception while trying to get the translation on the original entity without checking if it has one or not.
While trying to understand the issue, I realized that the only test on this method was from \Drupal\Tests\content_translation\Kernel\ContentTranslationFieldSyncRevisionTest::testFieldSynchronizationAndValidation() and that it doesn't seem to really cover this specific case.
I faced this issue using the above patch and translating entities containing link fields with TMGMT.
I don't know how to reproduce on a Vanilla Drupal.
Check if the translation exists before trying to get it. In case it doesn't, use the source entity to get fields values.
Active
11.1 🔥
content_translation.module
Opened a MR
Added a patch for composer
Still needs tests to showcase the issue (help needed here)