I gotta say I came in here to flex and I learned so much. I am going to roll some of these changes really soon once I find out where to best add them to my Hugo template. I'm going to reply to some of them below to clarify some things:

It may be worthwhile to experiment with adding some preload links to the html template? or output? like below and assessing if it makes things faster for you.

This is the most interesting because I didn't even know this was possible with HTML5, so I want to add this right away.

I have a pixel 6 and notice some lag in scrolling. Could it be that you don’t use srcsets but instead huge screenshots no matter the device screen?

The background is a large image in the CSS via background-image, I don't know how easy it would be to change it to a srcset but I will give it a shot

The fonts can be loaded from another file that ends in the cache, lowering load time next time.

At the very least they need to load last because they are the largest burden