Most browsers have a reader mode. Firefox has one built in, I just click the icon to at the right end of the URL bar and it does it nicely for me.

Try the reader view in chrome or Firefox. For chrome on android I automatically got a prompt to view simplified page

Wow, this works great! On Android I recall getting the "simplified page" prompt but never found that to be all that great of a solution but using reader mode with Chrome is pretty neat. You can format it to basically be the same as reading a book from the Play store.

One nit is that if I tab away from the page and tab back the highlighted area is wiped from the reader pane -- assuming I had unhighlighted it in order to start reading.

In Chrome it seems like clicking the pop up is the only way to access simplified view. If you exit, follow a link, tab away, whatever... I can't figure out how to get it back! Any tips? Really confusing that I'm either missing something obvious or the explicit option is missing.

On iOS you can click the icon to the left of the URL input and select reader viewer as well. Hides ads too.

You can use browser extensions to send articles (blog posts etc.) directly to kindle.

I am on mobile app at the moment so I don't have links for those extensions.

Safari, Firefox, and Edge all have a built-in Reader mode that doesn't exactly the thing you want for the device that you are on. Lots of extensions do this as well. There's used to be a handful of websites but it seems they no longer exist (they were also commonly used to bypass paywalls).