
The held spear uses a different sprite that's bigger than the normal one, but it is in the same folder as the spear, maybe you put a setting to only use 16x16 textures so that's why you're not finding it, try seeing if it's a setting or use a different editor like photopea or check which version of texture you downloaded.
EDIT:
I forgot to mention but you should also check if the version of your texture is 1.21.11