I see the script above derives from the defective Unity example code where they call .Move() twice in one frame. That will likely cause you ground detection problems in the future, assuming you rely on the CC to detect.
I wrote about this before: the Unity example code in the API no longer jumps reliably.
I reported it to Unity via their docs feedback in October 2020. Apparently it is still broken:
Here is a work-around:
I recommend you also go to that same documentation page and ALSO report that the code is broken.
When you report it, you are welcome to link the above workaround. One day the docs might get fixed.
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!!