Finally! A long time wished feature is implemented (if I don't misunderstand it). I am using original RetroArch UI on my desktop Linux PC (Wayland).
MENU: New function in Quick Menu: Add to Playlist
We can finally add games to a custom or any playlist, not just to the favorites! I was doing workarounds by renaming files and such to achieve this.
INPUT/KEYBOARD: Add support for multimedia keys
This is nice too. Doesn't sound much at first, but this means we can reassign some "useless" keys in emulation to do some specific things. This is remain to be seen how useful it will be.