I noticed that when I have the OptiFine mod installed, Show Me Your Skin crashes. Can this be resolved?

Optifine has many incompatibilities and isn't supported. Please consider alternatives https://lambdaurora.dev/optifine_alternatives/

To add to that, I'd support Optifine if I could, but it's closed source and invasive nature makes it basically impossible for me to do so.

All Optifine features have been ported as fabric mods at this point though, so there's really no reason to use it anymore.