I finally found a repro for the settings editor breaking entirely:

• have settings editor opened without query
• reload window
• when you see the default formatter change from null to an actual value click the dropdown (see video)
• leave the dropdown open while startup still goes on and things are restored, hover over the options
• click again on the dropdown to close it
• now try to click on entries in the ToC and notice that nothing works anymore

Might need a few attempts, see recording: