A texture pack replacing newer FurfSky Reborn textures with older ones (with permission from the artists of course).
It's pretty complicated to get helmets to work properly on 1.21.5+ with legacy packs like this, but I've found a way and gotten it to work.
Don't like a retexture in a newer version of Furfsky? Well FSL has replaced many of the new textures with older 'iconic' ones.