UK here and zero.
New build house that is using loop @switch i.e. the live goes switch to switch and the light fitting gets a single cable to the rose providing the switched live power from the switch.
It has made 1,2 &3 way lights really easy to convert.
Still uses ring rather than radial for sockets annoyingly.
I have found I can fit sonoff minis into both metal and plastic 35mm boxes. However, removing the box, wiring up in a maintenance free box with wago lever clips, put that in the wall cavity and feed a new cable for the switch only back into the box and doing it back up is a god solution.
Alternatively, put a single gang box at the same height as extraction fan isolation switches (almost roof) with a blanking plate and intercept the wiring there.
Yeah the loop@switch basically puts the feed from switch to switch, which is now almost universal to new builds because of how much it benefits downlight installations and how popular they are.
Only the switched live goes up to the roof.
In older houses, loop @ rose was common as a single twin & earth could go to the switch, with red/brown taking a live current to the switch and the black/blue taking a switched live back to the light. These should be marked with brown sleeving over the blue to indicate it's a switched live line.
In these instances (as commented by others) you can take down the ceiling rose and access the permanent live & neutral as well as switch wires from there instead.
Sounds like your house builder was very much "the old ways" though as it's really uncommon in new builds to still do it at the ceiling rose.