I have not seen any "illegal" fields in any of the screendumps.
What I do see is that some kind of strange software shows a picture as bytes instead of the picture.
Did you know that there is an action called
"Remove fields except" https://docs.mp3tag.de/actions/remove-fields-except
In this action you enter all the field names for the fields that you want to keep and the rest gets removed.
Yet, there is no "alert" - as the fields that you showed are perfectly legal and valid.
Like in the thread of your's
remove cover does not remove the tag field COVERART
it is now down to you to first take care of your files' structure and integrity.