I'm very sorry I obviously misread your response.
First back to the original problem. I added 3 screenshots and an export of my settings to show the process of editing and the result.
To answer your questions: All my music files are in one folder on a separate drive and all the playlists (M3U) are in the same folder. They existed there before I installed MusicBee in relative file format. When editing them I currently use the previously describeld process:
1. Edit the playlist in MusicBee
2. Export the playlist in musicbee to correct the file paths
Your suggestion with the MBP format actually works. When switching to that format all my playlists get deleted and replaced with the new format. I then can edit every single one to be automatically exported to M3U. The exported M3U actually has relative file paths. So basically that would work but it is a little cumbersome to have to do this to every single of my playlists and always have to remember to change that setting when creating a new one. If that potential bug with the absolute file paths and the M3U default format could be resolved it would prefer that approach.
Btw I afterwards changed back to M3U library playlists and the created M3U files then have the relative file syntax but as soon as I edit one in MusicBee again the absolute file paths are back.
ScreenshotsSettings