Anything holding back being able to define a cluster from the selected tracks?
Or fix adding album art to the “Unclustered Files” list. It will only accept it one track at a time. If any more than one are selected the artwork will not apply to the selections. But one at a time works all day long.
Nothing except somebody needed to implement it. Manually clustering a set of files is on my personal wishlist, but I haven’t yet looked into it. It’s likely pretty easy to implement actually. Not sure if there is a ticket for it.
I would consider it a bug that the album art dropping on multiple selected files does not work.