As quoted from the linked post.
It looks like you’re part of one of our experiments. The logged-in mobile web experience is currently unavailable for a portion of users. To access the site you can log on via desktop, the mobile apps, or wait for the experiment to conclude.
This is separate from the API issue. This will actually BLOCK you from even viewing reddit on your phone without using the official app.
Archive.org link in case the post is removed.
Users can block those on desktop without issue. On mobile it’s a bit harder so most people I know don’t even if they use ublock or something on their PCs/laptops (though that is of course only anecdotal).
So if anything if that was the issue they should’ve shut off support for the desktop version LOL /s