Howdy monocyclism,
(shortened version)
I'm sorry, I'm stuck on that one. I'll get back to you on that. But for the moment..the road from Flint to Prestatyn..I don't think there is anything other than main road A548. You can ride through Bagillt rather than use the by-pass.
When you get to Mostyn, there are traffic lights by the docks ,you can cross over and there's a cycle path for a mile or so. .
(If you send me your e-mail address I can do a bodge pic with google map with circles and crosses and other interesting details

)
Because next is Talacre...Either carry on along the A548 to Prestayn (and beyond) or...turn down to Talacre and follow a proper cycle path
(1mile) then through a campsite, out, through a golf course, then out and on the promenade at Prestatyn and a traffic free ride on to Rhyl.
Hope that helps in some way. I'm going to have a look for the cycle path from Connahs Quay to Prestatyn, but I think it is mainly road.
I will get back to you.
regards,
Elaine