(You can paste this into File Explorer's address bar to go directly there.)
Shaders are programs that tell your GPU how to render graphics. In emulation, shaders must be translated from the Switch's format to your PC's GPU format. Precompiled shaders are pre-translated shaders saved to your disk. This allows the emulator to load them instantly instead of compiling them on the fly, which prevents stuttering during gameplay. ryujinx precompiled shaders
The shader cache is stored in the following folder by default: (You can paste this into File Explorer's address