It’s probably also worth pointing out that certain fields will display ‘broken’ images if that field is unprotected.
So, for example, the FA field is protected by default so that users may add their own media if they choose. If this field is unprotected, it will display ‘broken’ media which may lead some users to believe that media files for that field have not synced appropriately, or that there is missing media, even though this is not the case.
For those fields, like FA, protecting that field will prevent those ‘broken’ images from appearing. There is a longer explanation here, but it stems from how Anki tracks its media folder and how it ‘points’ to its own collections. It’s a weird quirk of the software, ultimately.
A slightly longer explanation can be found here: AnKing Step Deck Wiki
It looks like MarcosZan otherwise did a great job of answering your question/s, but of course if there’s anything else on which we can help please feel free to reach out. 