The left side is the converted XML file. When I paste it into the file on the right, the quarter notes highlighted in green disappear, and the stems of the half notes split into upstem and downstem voices.
Even when I try to use Note Spacing, I cannot select the quarter notes.
How can I resolve this issue? What changes do I need to make on the right side to make it look like the left side?
In Engrave Mode, if you select the notehead, it looks like it selects only one voice (the downstem one, here). It allows you to change the Voice Column index (and to swap the voice order if needed).
(But I would rather use the Notation Option @Vadian is showing!)