Wasn’t there an old browser that would render the page on the server and just send down the result or something like that?

The old Opera for mobile did that. I think Chrome had something similar at one point.

Opera!

I’d love something like it for all my older devices where I can set it and forget it.

NextDNS is pretty good for this - just change the DNS in your network settings.

You'll also need to add bundles to block dns names ( free fyi)