Clutch not disengaging

I believe you are confused, that is "reversed." Sounds as if the clutch is ALWAYS engaged, and instead, is not "releasing."

Did it ever work right? That is "it did work" and now you are replacing a worn clutch, or is this a "new" build with new or used parts?

Might be a clutch problem, "new" does not mean "functional"

Might be pilot bearing too tight or even something bent, or maybe you have a crank not drilled deep enough, the pilot shaft is hitting "bottom."