Issues with matcap

I’m trying to sculpt a little something and bring it on Spline to embed it in a website.
My goal is to render it with a custom matcap that I made in Procreate.
Unluckily, the matcap won’t show smoothly on many parts of the sculpture… It’s probably a topology / normals issue, since I’m a self-taught, but I don’t really know how I can solve this or either avoid it in the future. Both the blade and the bottom of the handle looks very warped, while the small etching holes on the handle looks great. How can I make the shading even? Thank you in advance!!