There is google compression https://github.com/google/guetzli
Guetzli. Looks like development has stalled? Perhaps for just that reason.
I've never had much luck using jpegoptim. In most cases it's only removing the metadata, which isn't much on high-res files.
Guetzli is nice, if you don't have too many images to recompress (quite slow): https://github.com/google/guetzli
Turns out there is a project which does that: https://github.com/google/guetzli
You know. I was actually quite annoyed ( to say the least ) with the post. For one the post is lacking a date, and you have to search yourself it was published in April 2017. And without a date the article is completely lacking context because Guetzli [1] hasn't been worked on for 5 years. And as [2] mentioned its work and derivative was ultimately merged into JPEG XL, which is a very decent image format. ( People should definitely check out JPEG XL if it is not on your radar yet )
But then I notice it was Dan luu who submitted it, which likely means there must be something much deeper than is what is shown on the surface. So what is the context here ?