Perhaps this has been asked and answered somewhere else, but is it possible to keep the "font subsets" to optimize loading of font files similarly to how they are loaded from the Google's CDN?

Looking at the code, this part that is now removed:

		if ( 'cyrillic' === $subset ) {
			$subsets .= ',cyrillic,cyrillic-ext';
		} elseif ( 'greek' === $subset ) {
			$subsets .= ',greek,greek-ext';
		} elseif ( 'vietnamese' === $subset ) {
			$subsets .= ',vietnamese';

Seems that loading /open-sans/font-open-sans.css will always load all Open Sans font files, Cyrillic, Greek, Herbew, Latin, Vietnamese, etc. which won't be needed on all sites. Ideally the CSS should be split in few parts/subsets and only the needed font files will be loaded by the browsers.

@azaozz The Google font stylesheet already includes all subsets even if the URL specifies only latin and latin-ext.
https://fonts.googleapis.com/css?family=Open+Sans%3A400italic%2C700italic%2C400%2C700&subset=latin%2Clatin-ext&display=fallback

The Google font stylesheet already includes all subsets even if...

Yes, what I am asking is if it is possible to include only the needed subset(s). There is no point in the browser downloading all 64 font files on every front-end page load. This seems like a considerable slow down and a large amount of unneeded files, wasted bandwidth, etc.

Looking at https://fontsource.org/fonts/open-sans and the repo at https://github.com/fontsource/fontsource/tree/main/fonts/google/open-sans, there are ready-made CSS files that can probably be adjusted and used. For example: https://github.com/fontsource/fontsource/blob/main/fonts/google/open-sans/400.css (the .ttf and .woff font files for the whole Open Sans can be downloaded from the first link).

There is no point in the browser downloading all 64 font files on every front-end page load.

Very rarely will the user agent download all fonts. That is why the unicode-range tag describes the characters defined in each file, so that the browser/user-agent can decide weather that font file is needed or not. Same with the weight descriptor.

See: https://w3c.github.io/csswg-drafts/css-fonts/#font-prop-desc

For a font family defined with several @font-face rules, user agents can either download all faces in the family or use these descriptors to selectively download font faces that match actual styles used in document.

Also: https://caniuse.com/font-unicode-range