Chrome has had a builtin DOM distiller for a while (not sure if still guarded by an experimental flag, on my phone now so can’t check), but it’s primitive and worst of all reloads the page on exit.
Firefox and Safari have decent reading modes, though.
Um, it’s not? Chrome 78 on macOS here, text is rendered in 14px Roboto, content box width is 75% (on 2560px viewport). I find it fairly pleasant to read, my only problem is page reloading on exit as I already mentioned.
Edit: The mode is gone after updating to 79, seems to be gated by a command line switch now. What the hell.
I just updated to Chrome 79 and now the distilled mode is gone. For anyone who's looking on how to re-enable it, here's a thread: https://support.google.com/chrome/thread/22576539