Install flush-mounted boxes flush or with a gap

The flush-mounted switch boxes as well as flush-mounted junction boxes are always set slightly outward so that after plastering the boxes align as flush as possible with the plaster.

Switches or sockets belong in the flush-mounted box and not in the plaster.

Instead of the cover proposed here, one can also resort to the well-known method of crumpled newspapers which are placed inside the boxes. Even if the boxes are covered by plaster, they can still be seen through the plaster. Unless the plaster is applied very thickly.

Set it back a little, otherwise you have to replace the supplied device screws with the long version for every box.

It doesn't cost much extra in terms of materials, but it's avoidable fiddling. Your electrician would hate you for that :)