Not as far as I am aware as this is when the DRM is run, as well as base assets and libraries loaded. WC3 always had this period but I think the DRM and additional complexity from Reforged has made it longer and more noticeable. I think it was just a black screen before.
To directly load map files you need to pass the DRM check. This requires you login to the WC3 client every ~30 days, even if just briefly (start from app and immediately exit at main menu). All Blizzard games are like this when running in offline mode. Steam games and the like are no different, this is just how modern games work sadly so it is not something you can be particularly mad with Activision Blizzard for.
In older patches the main menu background would briefly show up before moving to the loading screen.
Not all modern games, just look at GOG. Also let's not forget this kind of DRM was not in 1.31 and this version was overwritten to the inferior 1.32 for a lot of people who haven't even bought reforged.
