Ok. Bit of work but…
@Mattkmmr just posted a Shared Y-DNA that would do the 1st stage. It is so new that you’d have to add it manually. It hasn’t been pushed into the Plugin Manager system yet. It still needs some tweaks. It should be moved from General filters to Descendant filters. And it could use an Inclusive: Include selected Gramps ID checkbox like the “Descendants of <person>” from Descendant filters. )
Copy the ID of the Ancestor (to save a few steps)
Start by creating a Person custom filter called SharedYdnaLine
Add the following rules:
General filters: Descendants of <person> sharing yDNA
paste the clipboarded ID for the value
General filters: Person with <Id>
paste the clipboarded ID for the value
Set Options to
At least one rule must apply
Use that filter’s output to feed a second stage filter:
Ancestral filters: Children of <filter> match
set the Filter name value to SharedYdnaLine
General filters: Person with <Id>
paste the clipboarded ID for the value
Set Options to
At least one rule must apply
If you don’t include the Person with <Id> rule in both filters, you’ll miss people in the top generations.
If you need the mothers, swap the Person rule in the 2nd-stage filter with:
Family filters: Parents of <filter> match
set the Filter name value to SharedYdnaLine