How do i make a groundcheck for a 3d game?

alright, so here's the thing: i have no idea how to make a groundcheck thing.

raycast is unreliable because if you are standing on the edge, it simply won't detect a thing.

spherecast bugs out (for example the scene has the main ground and a bunch of slopes and cubes. and while it only detects the ground, it gives you a big "f##k you" if you are standing on a slope, if you are on the cube or if there's another mesh inside the main ground).

the only sane option i found is "OnCollisionStay/OnCollisionExit". and then again, everyone who uses that method uses tags, whereas i want this thing to be more or less universal like in most games (half life, quake, whatever other game).

so for the third method i understand that i should somehow get an angle of the collision, and if it's more than "x", i simply shouldn't count the detection. but i don't understand how do i measure that angle, since i'm not really familiar with api yet. and if this method is shit, can anyone please give me an advice? i'd really appreciate that