This seems to be a new issue with the desktop client.
As of today I am no longer able to play an entire folder directly, but only playlists. This is quite a big issue, since now I cannot mix several playlists together anymore and play them as one.
In the folder view the play button is still available, but does'nt do anything anymore. Same with double clicks on folders.
I am aware that this feature never worked on mobile.
Please fix this and stop removing features I use for once.