Apple ecosystems generally offer excellent out-of-the-box support for Southeast Asian scripts. Fonts like Khmer Sangam MN and Khmer MN come pre-installed.
Finding high-quality, Unicode-compliant Khmer fonts requires sourcing from reputable type foundries and open-source repositories. khmer supplemental fonts
Not all supplementary typefaces are created equal. Here are the industry standards currently shaping Khmer typography. khmer supplemental fonts