Playlist shuffle

I have been trying to figure out how to do this and can’t find an answer when I search:

I have box sets of 3 different tv series I will call A,B and C in 3 separate folders. In “settings/playback” I choose “shuffle” and can then “select/hold” on an individual folder (say A for example) to play the shows in that folder randomly. I would like to put all 3 series into 1 folder and be able to “select/hold” that folder so that it will play all 3 series randomly, together (not sure if that makes sense). Right now, when I make a new folder (titled “all 3” for instance) and drag either all 3 folders (A,B and C) or all the individual shows of all 3 series into “all 3”,  that folder is not selectable for “playback as playlist” so I can shuffle all of them.

In addition is there a way to set “settings/playback” to play “shuffle” for one folder (A for example) and as “list” for another series (B) so that series plays in order.