Two ideas:
-
collider does not match the graphics (look in Scene window)
-
you’re not moving it properly, perhaps pushing it into the ground
Either way, is your goal to learn how to make a player controller or do you just want one?
If you would prefer something more full-featured here is a super-basic starter prototype FPS based on Character Controller (BasicFPCC):
That one has run, walk, jump, slide, crouch… it’s crazy-nutty!!