Tools / Measure / Split measure, and dragging a bar line, seems broken in MS3.6

According to https://musescore.org/en/handbook/3/measure-operations i should be able to split a measure using Tools / Measure / Split measure.
However, for the attached score, that is always greyed out and does nothing.
Alternately, i'm supposed to be able to drag a barline over to a note, but that does nothing.
The following DOES work: select note, then hold ctrl and click on the barline in the pallet.
Yay! at least i have a way to do what i want...

I tested the above methods on a brand new score with a small number of notes added (two staffs).
Tools / Measure / Split measure seems to work reliably. Dragging a barline to a note sometimes does nothing, and sometimes splits only the staff where i dropped it.
Ctrl + bar line seems to work reliably.