If you download a custom version of the resourcespack through darkomizer.com, there is an error "Resource reload failed" on version 1.21.7 (fixed by copying the files minecraft/shaders/core/ of the default version of resourcespack). Also after fixing does not work custom font color (font color in my case should be black):

I forgot to add the latest version. Thanks for letting me know.

The new version is now available with the entry 1.21.6+, which is compatible with 1.21.7.