Two icon entries I have added to the SMPlayer main toolbar are "Add URL(s) (pl_add_urls)" and "Remove all (pl_remove_all)".
f I go to "Preferences > Playlist" and uncheck "The playlist window is dockable" and click "Apply", the above two entries vanish from the main toolbar and are no longer listed in the "Available actions" section of "Edit main toolbar".
It looks like other entries also disappear from the "Available actions" list.
Using 32-bit portable SMPlayer 23.6.0 obtained from the SMPlayer website. Also happened with 22.7.0
Windows 11
My work around is to just keep "The playlist window is dockable" selected but thought I'd mention it here in case someone might be interested in checking it.