I can no longer use F8 commands to say, change my crosshair size or change graphics settings (to turn my shadows off)

[FSSynthetic]

I believe this has to do with a recent update with FiveM. All you have to do is open the settings when in the server list and click on the Release Canary (Experimental/Unstable). Once you do that, restart your FiveM client and the issue should be fixed.