It depends on your app / browser—I’m using Arctic on an iPhone, and it has a setting to always open links in reader mode by default.
But usually there’s a button / icon / menu option once the site has loaded to switch to reader mode. This is what it looks like in Firefox on iPhone:
AlchemicalAgent@mander.xyz 5 months ago
I use Fennec for Android and that page has no ads that I saw. Phys.org also has a high factual and reliability rating on some independent rating sites.