On 13/01/2021 17:12, Another John wrote:

I seem to remember seeing words of caution, in here, about drilling
through the frame of a uPVC construction: any words of wisdom on that
for me, please?

When I was an aerial and satellite installer this was an absolute no-no.
Drilling a PVC frame led to all sorts of bother: warranties, leaks,
cracking, etc.
Normally we'd drill through the wall nearby, or drill into the mortar
joint at an angle at each side of the PVC, thus making a curved hole
that a stiff draw wire could get though.
Doorbells should be mounted on masonry adjacent to the frame, with the
hole going right through. Mount the bell on a nice-looking wooden
pattress if necessary.

Bill