There are also simple keyboard options to add and delete values from the lists right in the tag panel, without the need to open the options panel and submenus.
Use Shift+Return to add the value to the list
Use Shift+Del to remove the value from the list
From the change list for v3.20;
NEW: added keyboard shortcuts Shift+Return to add and Shift+Del to remove custom list values via Tag Panel. (#58937, #60411)