Mulch tree roots and mix with topsoil

Makes sense.

Rake in mulch.
Sow grass.
Roll in.

Mulch for covering (keeping moist) and working into the garden soil is useful, but not where the grass is going, because it pricks when walking barefoot and that lasts at least 2-3 years.

Delivery of extra topsoil is, in my opinion, unnecessary. We simply placed a lush green lawn into the building landscape without such delivery. No turf, classic sowing.

I brought it up because it is pure forest soil and not classic topsoil from building land. I see a significant difference there, but of course, I cannot make a final judgment from here. However, the garden landscaper on site could.