Applying Spar urethane on awning type window jambs

Newly installed, Pine,(exterior vinyl clad) window sash piece was not factory finished. Do I apply Spar urethane to the jambs and sections that close against the frame? Information found online only dealt with "Not Painting Double Hung wood windows, so they move up and down, freely"
I’ve already sanded and stained any wood that risks exposure to elements, hopefully reaching all crevices. Factory booklet also only deals with double hung windows.
Thank you for any help!