Also Google still cares about serving the correct font version depending on your browser and OS, e.g. by not sending variable fonts (where one font file covers

Also Google still cares about serving the correct font version depending on your browser and OS, e.g. by not sending variable fonts (where one font file covers multiple font weights for example) to old browsers that didn't yet support them. People self-hosting Montserrat are one bane of older browsers, because that seems to be a relatively popular font that got converted to a variable font file at some point, and which in browsers without variable font weight support then gets displayed at the thinnest possible font weight, which is really thin. (I concede that this is a niche complaint, but still…)