I know you need multiple subs for different movie versions. Example: All "MySistersHotFriend" 2160p have a different intro than 1080p.

This is a direct translation
https://www.avsubtitles.com/subtitles.php?subid=43286&revid=20250627101958
of my subtitles

@miroshopa: Thank you for keeping my credits. :-)

And this is another version:
https://www.avsubtitles.com/subtitles.php?subid=39726&revid=20250623083318

They are a little different:

9
00:00:25,060 --> 00:00:26,126
Хей, какво става?

10
00:00:27,120 --> 00:00:28,020
О, здравей, скъпа.

11
00:00:28,580 --> 00:00:29,460
Къде е баща ми?

and

8
00:00:21,640 --> 00:00:26,080
- Хей, какво има?

9
00:00:26,080 --> 00:00:29,080
- Обичам те, скъпа.

10
00:00:29,080 --> 00:00:29,920
- Баща ми.

Keep two versions?

Another question: IF the original author (miroshopa) would want to delete one of them, how would that be done?

Yes, keep both version.
Many users don't even try to sync dialogs, so having several versions with differents sync is useful (and sometimes, the video cut is also different, so keeping the versions is mandatory).

A user can't delete a file himself, even if he is the original uploader. He has to reach admins by the contact form, then it depends on what he really wants:

- Delete only the current revision and go back to the previous one
- Delete the subtitles files (and if there's no more subtitles, the movie entry will be deleted as well)
- Keep the subtitles on the site, but associate them to the "no-owner" pseudo-user.

I'm the only one who is able to do this, because the tools to do that are not available in the admin menu.

You don't need to invest time for me in this matter, because I can live with multiple subtitles. Even if some should be with wrong timings are (small) mistakes.