Variable fonts similar to Google Material Icons render broken when using the default Cocoa CoreText backend, but render correctly when using FreeType.

Variable fonts similar to Google Material Icons render broken when using the default CoreText backend, but render correctly when using FreeType.

This is a font file MaterialSymbolsOutlined[FILL,GRAD,opsz,wght].ttf provided by Google’s official GitHub repository. The variableAxes in the code looks like this:

font.variableAxes: {
    "FILL": 1,
    "GRAD": 110,
    "opsz": 26
}

Additionally, I have recently discovered that when the value of FILL is set to 1, both font backends exhibit issues that do not meet expectations. With CoreText, the GRAD, opsz, and some other attributes differ from the standard implementation (resulting in distortions or partial effects). With FreeType, only the FILL attribute has issues.