I worked with someone that fitted a combi boiler with threaded rod that went through the wall and had washers and nuts outside.
It was on an old house near 7 Dials with one of those walls made of flint and horse crap :)
Boss wasn't impressed, but the boiler wasn't falling off the wall.
I struggled to find some fixings that are for dry lined/ dot & dab walls a couple of years ago.
Screwfix and builders merchants didn't seem to stock fixings specifically for dry lined walls.
Is the correct answer.
This is what I have done, 2 X 1 baton, and I painted it before fixing to the wall.
Used screws and Gripfill, made sure the Gripfill was dry before fitting the curtain pole.