Story #69617: FormEngine bugs
Unable to edit file metadata
Due to change https://review.typo3.org/#/c/43485/ it isn't possible to edit the metadata of a file anymore.
The field "file" is defined as label field of the table but is not used in the types definition of the table sys_meta_data. That's why it was removed from the processedTca before that patch and wasn't handled furthermore.
Now the field is added to the processTca of the record and the file field is converted to an array.