If you want to stick with the old-school PNG icons, we open-sourced `icopack` - our internal tool for efficient packing of individual PNGs into a highly-optimised ICO files [2].
[1] https://optidash.ai/blog/optimizing-favicons-for-the-worlds-...
The post you linked to doesn't include the word "SVG". Is there a separate article that compares using one SVG file vs. using multiple images?
It's hard to imagine that using a typical suite of PNG images at different sizes is going to be more efficient (and future-proof) than a single SVG file run through svgo.
That's the wrong comparison though - each browser will typically only download one favicon size.
Earlier this year I created my own ICO editor for fun [1]. I learned a lot about reading and writing binary files, and decoding BMP data. While testing the editor on existing site favicons I kept finding that they were all uncompressed BMP data, and came to a similar conclusion to your article after checking the icons used on the Alexa top 100 sites.
I guess this is a combination of the ICO format being somewhat opaque (it's hard to tell if it's using BMP or PNG without using a hex editor), and that there aren't many applications available that create PNG-based ICO files in the first place (especially ones that are used in web development pipelines).
1. https://ico-editor.lach.app/ - Client-side ICO viewer/editor, can open and convert BMP to PNG.
PS. I noticed that your own site's favicon is uncompressed.