Dorico 3 added a new option to place alternate fingering vertically and without parenthesis or italics. This was to allow the style of alternate fingering in which a line is inserted between the numbers. However, the two numbers are placed too close together to allow a line to be inserted. Were the two number a little farther apart, this option could solve most such instances.
The example shows the present placement of the alternate fingering numbers and the suggested placement with the added separating line:
The user would add the line, not Dorico.