Forge only supports the way the Vanilla launcher works, no special support for other launchers.
It's unfortunate that pack devs get caught up in this, but if you're looking for a way to distribute packs we usually recommend CurseForge as it's where most mod devs upload the mods themselves.
At this time Optifine has a monopoly on shaders.
Sorry I came on a bit strong, the more people ask this question the more annoying it gets that they seem to think open-source Forge needs to change to fit closed-source Optifine
Not our problem.
An open-source project and a closed-source project are incompatible, why do you assume it is the open-source project's responsibility to become compatible with code they are not allowed to see?
Is this the error?
GLFW error before init: [0x10008]Cocoa: Failed to find service port for display
If so you're out of luck for older versions as Apple decided to say "To hell with backwards compatibility" with their new stuff so 1.16.5 and previous aren't compatible.
1.16.5 is not compatible with Java 16, if you still have Java 8 installed you can use it by invoking the full path to the java executable instead of just invoking "java" and letting your computer pick which one to use