Thanks to @alecxs and @Izzy I realized that the problem was related to the folder and subfolders attributes (permissions, owner and groups).
I will tell you what I did to restore just a specific application from the NANDroid backup generated by TWRP (without using any command but root is required)
Add .tar to the .win000 and .win001 etc (ignore the .sha2 ...
I have been using Playlist Backup on older Androids, and it works well. It creates a text file for any playlist backedup and can be found in the "PlaylistBackup" directory. Please confirm if it works on newer phones.
I still don’t know where the files are stored, but for others with same wish for text file-backups, the app: "Playlist Manager" can do the job.
It basically has a "Share A Playlist" function which allows you to share in text format.
It would be helpful to be more explicit in what you're doing, like specific adb commands, although I think I'm running into the same issue.
I believe what's happening in your situation is that you're (unintentionally) taking a backup of the Owner user. Since you are in the secondary user profile, you will not see the prompt to start the backup for the Owner ...