IIRC, it’s a bit complex due to backwards compatible settings. If ~/.nv exist, the old 128MB are applied, if the new ~/.config/.nv (or similar) is used, 1024MB. Something like that. Somewhere in the forum, there’s a post by aplattner, explaining things.
Increased the default size for new OpenGL/Vulkan Shader Disk Cache location to 1024MB. Note that caches with paths containing "/.nv/ will continue to use the previous default of 128MB unless the size is manually overridden. For more information see the “OpenGL Shader Disk Cache” section in the “Specifying OpenGL Environment Variable Settings” chapter of the README.
Cache path for my systems appears to be …\nvidia\GLCache. I will assume 1024MB based on spec above.
A future project will be finding a method to use nvidia-settings without X, for inspection of this value, assuming nvidia-settings can inspect this value. There are guides for nvidia-settings in headless mode. Unfortunately they all rely on X being present on the system.