For some reason, in the 1.21.130 update (Mounts of Mayhem drop), the spear appears to be clipping thru your minecraft character. Additionally, the spear also appears clipped in first person; In fact, it appears to not be held properly.
The pointed tip is not facing the right direction too, as it’s facing backwards, and from your POV you can only see the stick of the spear model.
Under this im gonna share some screenshots.
Same issue happened to me. It clips through when I use a custom avatar, but works on classic skins…