Why shouldn't those details be editable? I know I've seen requests specifically asking for that functionality.
Bug [ ]: Library Analyze view - Details tab's fields are editable!

So you can edit the ratings and the names and the result and the date! No way.
This bug has occurred before and been repaired. It needs to be fixed.
Here is Analyze of an Archive game, with all greyed out fields, indicating note editable:
The same should go for Library collections.

Our current logic says that if “Site” is set to “chess.com” in the PGN, meaning the game was played on the site, then all details except Title cannot be edited. However, you should be able to copy the game and make changes to the details. I don’t think there is a sure way to prevent downloading and re-uploading PGNs while allowing customization. The original game details in archive will never be affected by these changes. Open to improving something here, but there will always be ways to make convincing/deceiving games.

Our current logic says that if “Site” is set to “chess.com” in the PGN, meaning the game was played on the site, then all details except Title cannot be edited. However, you should be able to copy the game and make changes to the details. I don’t think there is a sure way to prevent downloading and re-uploading PGNs while allowing customization. The original game details in archive will never be affected by these changes. Open to improving something here, but there will always be ways to make convincing/deceiving games.
One can modify Chess.com game's Detail info in a library collection.
Yes, one can always edit the pgn and create a tampered games.
Allowing an interface for tampering with the details is just plain wrong. Currently saving a Chess.com game to the library collection results in an interface where the chess.com details can be modified.
It is a bug. Just make the fields un-editable.

I'll test later in a full browser but I just tested and leaving the tab after making changes and loading it again results in the changes being lost.

I'll test later in a full browser but I just tested and leaving the tab after making changes and loading it again results in the changes being lost.
You did not do a save.

I was testing on the results field which resets
No, not if you do a save.
Edit Details Result to Draw and Save yields this:

I see the confusion. We released some Analysis updates near the same time as these Library updates so this seems related to Library but is actually Analysis specific. I can confirm that right now Analysis allows editing of details for games where the site is set to chess.com which is a bug as far as I know. I'll make sure the bug is surfaced with the Analysis team, thank you for reporting and for your persistence when I misunderstood! 🙌
Detail fields should not be editable. The game result is even editable!
Below you can see the xxx's added to the fields. Saving the game save these edits.