Unless I'm mistaken, cue points, loops, are saved in Serato's database. I don't believe there is a way to apply them to a new (updated) song file. They will not be in the ID3 tag.

the email from serato:
Marcus S (Serato)

Jun 9, 2020, 9:58:14 PM GMT+12

Thanks for your email. Please firstly note that saved beatgrids cannot be transferred between re-encoded tracks, as this information is not stored in the ID3 tag but rather in the _Serato_ folder alongside other Serato library info. If they haven't been edited, you can still get the same beatgrid back by just analysing them

For .mp3 files the cue points are stored on the ID3 tag - so I recommend that you get in contact with MP3tag themselves as it looks like the cue points have not been successfully copied.

This is not correct. Cue points are saved to the files themselves via ID3 tags.

Thats what I thought, but inspecting the id3 tags, I cannot find anything about it, and thats also why I could not copy the cue points to new tracks

Correct. What are you using to inspect the ID3 contents?

First I used Mp3Tag, which I was intending to use to copy the tags to the new tracks. Then I used Audacity, but still didn't see anything

Mixed In Key has an ID3 editor and it may be worth the time as MIK itself actually has one of the most advanced cue placement tech I have seen. Not the Auto cue which when used properly is a marvel in itself (for some genres of music) but they actually have a click & drag features that lets you literally view cue points and move them around as you please. Perhaps Metabliss (as it is called) can assist with this? Probably not but worth a shot.

Hi Jannik,

Are the "higher quality"-files still MP3s?

If they are FLACs for example, the cue points have to be saved in the _Serato_-folder instead according to Serators mail.

Yes they are still MP3s