Cutting slots for wall lights

Hello everyone,

I hope I am in the right place with my request.
I bought a house built in 1992. Exterior walls are 17.5 cm hollow bricks? the red ones.
Now I want to attach two wall lights on a wall in the living room (exterior wall).
For this, I planned to chase a slot 15 cm below the ceiling horizontally. Length approx. 4 m.
Now I accidentally read something about the guidelines for chasing slots on the internet.
Now I have some concerns.
Is it safe to carry out the slot as planned?
What alternatives are there? Ceiling and floor are finished or should not be damaged.

Thank you in advance.

Alternative: Cable duct directly under plaster, not chased in, only glued/nailed

If applicable, the plaster thickness for the [Bj.] is also sufficient. I would do it that way too. But no conduit wiring, just regular NYM.

I can't fit the normal NYM in the plaster. What is wrong with flat cables?

If the required 10mm plaster coverage for [Stegleitung] can be maintained, then also, but then you might as well just lay NYM.

Why the 10mm plaster cover?