Old info:

A user of the MumbleLink mod reported this to me and I did some troubleshooting. I think the issue is somewhere in OptiFine's code since all of my MumbleLink code gets initialized properly.
Here is the original issue that includes logs and more info: https://github.com/magneticflux-/fabric-mumblelink-mod/issues/32

New info from @Chocohead:

Setting java.awt.headless=false causes OptiFine to silently fail to start if mipmaps are not disabled. OptiFine incorrectly uses AWT's Dimension class to calculate mipmap atlas sizes.

I might have a hack to work around it here: https://github.com/magneticflux-/fabric-mumblelink-mod/pull/33

You could write a transformer that replaces all references to java.awt.Dimension in OptiFine with a custom class, but a better solution would be fixing it at the source: sp614x/optifine#4980