How should I input this kind of sheet music?
It is separated into one measure with a 2 instead of a 3 and a cue.
I have often thought about this myself, as many 19th Century orchestral parts use this appearance for short anacrusis-type cues at the end of a multi-bar rest.
In your example, it would be feasible to enter the two cue notes as grace notes (without the slash) on the first beat of the bar after the 3-bar multi-rest and scale them to cue size in Properties > Common > Scale. Enabling Grace note before barline in Properties > Grace Notes causes the rest to split, so a method that works is to nudge them left in Engrave mode > Note Spacing using the circular edit handle, not the square one, and space them to your taste at the same time. It would probably be wise to also enable Suppress playback (in Properties > Common). The cue label (Vl) would need to be added as staff-attached text attached to the first note after the barline and nudged left in Engrave mode, and also have its font and size manually adjusted to match any “real” cue labels elsewhere in the part.
For longer cues, this method would very quickly become tedious with regard to the amount of manual adjustment needed and potential collisions/overlaps (as these fake cue notes are not really “in” the bar where they now appear).
My experience over many years (50+) of reading from parts where this type of cue occurs is that it overwhelmingly seems to be used for very short cues like the one in your example.
Thanks for the detailed explanation. That solved it for me.