"preparing textures"

I’m trying to open a 4.26 project in UE5 and I have this message with more than 4500 textures.
It’s using all my CPU (I7 7700K) and it takes 2 hours to “work” on 100 textures.
Is this a normal behavior? Why does it need so much “calculations” to use textures from 4.26?

This should be normal behavior as long as this is a one-time calculation after loading the map for the first time. The Unreal Editor has to “build textures” before using them.