Empty conduit from the supply room to the attic 50mm - sufficient

Why should it be filled out immediately? It defeats the purpose of an empty conduit as a reserve

Airtight only when necessary...

A conduit from the connection room -> attic is generally to be recommended, but planning from the outset to fill it up? Why not just lay the cables in the planned number right away?

And glass wool does not seal, it must be sealed airtight!

In my opinion, a conduit makes sense because cables can be easily replaced or additional cables can be pulled through if needed.

We were told that completely sealing it is not sensible. Condensation can form inside the pipes (especially after new construction). If the conduit is sealed, water accumulates inside it. At least that was the experience of our electrical company. Whether this is really the case, I cannot judge due to lack of experience.

Well, at least during the "wet" phase of interior plaster and screed, I would completely tape off the empty conduit. We forgot and promptly had mold in the roof truss at that spot because the moist, hot air rose up there.

I would not rely on being able to "effortlessly" pull new cables later, unless the cable can be laid without any bends. Nevertheless, I would definitely pull ALL cables immediately and only lay empty conduits as reserves (possibly with a pull wire). Don’t forget the PE for the satellite dish!

Well, I have a 50mm HT pipe plus two M25 pipes (not those flexible cable protection hoses) - they go straight down.

You can always get them through.

Our site manager also gave the tip that the empty conduits in the attic and basement should be completely sealed with expanding foam. As always, three experts, four opinions. I will probably stuff some foil in there and then seal it with expanding foam. The foil is to prevent the expanding foam from penetrating too deeply and later, if you want to use the empty conduit, you don't have to cut off too much or risk the expanding foam migrating too far into the conduit. Or does anyone here have a better tip on how to prevent foam from expanding too deeply?