You can put a disc into the portable jukebox while its in your inventory and it will play it.
You can even place it on the ground.
Like that it will work as a regular jukebox.
One portable jukebox can hold only one disc,
but if you use more portable jukeboxes then you can play more songs at the same time.
Only you hear the song if played from your inventory.
The song is on repeat while the jukebox is in your inventory.
And you can see what disc it holds and shows the name of the song too.
Mod Currently Supports:
Forge 1.21.5 | 1.21.1
Fabric 1.21.6 | 1.21.5 | 1.21.1