An Odd Question About Map Randomization

Godot Version

v3.5.1.stable

Question

I’m mucking about, trying to learn how to make top-down ARPGs (Think; Diablo, Path of Exile, etc.)
But…I can’t find information on HOW those games procedurally generate maps.
Do they have ‘tiles’ that they mix around and link up?
Is everything just generated on the fly, instead of using tiles?

And furthermore, as I am basically paralyzed with confusion; What assets in the Asset Library could help me practice any sort of randomizing of maps?
Because I do not know where to start looking.