[NEWBIE] Question about "GameMode" and spawning

I was following this YT tutorial

But… the “BP_FloorTile” just do not spawn

At first I try this

Its works! but then I change it again to another name… then its doesn’t works…

so I changed it again to “ThirdPersonGameMode”
but… this time its doesn’t fix it… now I’m stuck…

Why is that? can someone explain it to me?

There is also this

I have checked that in “project settings” I choose the right game mode, but I just can’t find where is the “world setting”.

Basically… I want to know how “GameMode” works in this case and how to spawn the “BP_FloorTile”