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.

https://web.archive.org/web/20230611224026/https://old.reddit.com/r/help/comments/135tly1/helpdid_reddit_just_destroy_mobile_browser_access/jim40zg/

  • It’s all part of the plan to make their horrid app experience the only way to view Reddit content on mobile, in order for them to get not just some user data, but ALL the user data.