I am seeing this same issue, however it is limited to fonts that I have installed on my local system. Fonts that I do not have locally installed are getting anti-aliased just fine but fonts that I have installed on my PC are not being anti-aliased. I have tested this with several different font families and the behaviour is consistent.

Opera: https://ibb.co/f27O5Q

Chrome: https://ibb.co/e9twQQ

I too have tried all of the flags as well as purging my browser settings. The only thing I haven't tried yet is reinstalling, however I am seeing this behaviour across multiple devices.