One thing this article doesn’t mention is that the two font file formats used on the web (TTF/OTF and WOFF) can’t contain more than 65,536 glyphs. Which I suspect is the main reason the Noto font caps out at ~64,000 characters on that bar chart of how many characters are in some fonts.
And not only is that not enough for all of Unicode, but you actually hit the limit much sooner, because that is the number of glyphs, and a good font has more glyphs than characters, due to things like ligatures.
https://www.w3.org/TR/2018/REC-WOFF2-20180301/#DataTypes