You requested the page from their server so they know you visited. Setting a cookie doesn't do anything unless you come back to the same site, at which point you request the page and they know again anyway.

That assuming e.g. your IP address doesn't change. Cookies can be used for tracking - in this case they aren't though, the cookie for me is "resolution: 1920,1", which is set by this inline script:

    <script>document.cookie="resolution="+Math.max(screen.width,screen.height)+("devicePixelRatio" in window ? ","+devicePixelRatio : ",1")+"; path=/";</script>

I can't tell what it's used for (seems unused in the other JS files), but as far as cookies go, that seems pretty benign.

Feels like the kind of thing one would write if they wanted to keep track of whether to serve you "retina" @2x-sized images in the future or something.

In fact, that's pretty much what it is. This looks like it comes from an older version of the Adaptive Images WordPress plugin: https://wordpress.org/plugins/adaptive-images/ (there's a very similar version of this code in the adaptive-images-front.php file).

The WordPress install would use this cookie to resize an image to send to your browser.

Could that itself be used for tracking? Sure, but you'd need at least a few other signals as screen size and DPR aren't all that unique across most devices.

Not quite the same. With email pixel tracking, anyone can theoretically obtain your broader geographical position just by sending you an email via Superhuman.

Yeah. I guess they try to offer the customer something extra. But this doesn't look like to be the thing they should offer.

In order for pixel tracking to work, one has to open the email and load the pixel. I don't think you can track someone just by sending an email.

This has been the case since always. It just wasn't as obvious to users because consumer-oriented mail software didn't include it.