Some fields like the image field, for example, have sub-properties that can be set as translatable or not( title, file, alt tags)
They do this by adding "column_groups" to the field definition. Attached is a patch that respects this for the Default Field Processor
In my use case, it wasn't the image field I wanted this for but for link fields so I could disable automatic translation of the urls but leave the titles translatable. Core doesn't provide this, but I did this just by altering the link field definition to have appropriate "column_groups" properties. Then I can disable the URI for translation and TMGMT will only translate the title. This patch alone doesn't fix my issue completely as the link field still need to be altered but without this, internal link uri values like "entity:node:1" get translated to "Entität: Knoten: 1" and this instantly breaks that node. I am not sure how others are getting around this. I understand some people may want to translate the uri but the automatic translation should not do that.
Needs review
1.0
Source: Entity
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It's likely this issue predates Contrib.social: some issue and comment data are missing.
I have updated the patch a little to actually check for column_groups on the field definition and provide defaults, similar to how content_translation.admin.inc does it. That way if the translation form has not been submitted this should still obey the underlying field type definition configuration.
I also converted the patch into a merge request so it is easier to update and maintain.