If the website doesn’t work as it should on a phone and it tries to force using an app, there is a problem with the website. Using apps for websites is counter-productive and ridiculous. While the company has not revealed why it is putting a block in place for some mobile users, it is likely that it wants more information about its users to boost registrations and revenue on the site. Reddit wants users to use the app on mobile or sign-in at least. Others may see the list of topics in a subreddit or the homepage, and any tap on a link opens the dreaded sign-up page. In that case, Reddit states "to view posts in r/*** you must continue in the Reddit app or log in". This forcible action has annoyed a lot of netizens. It appears that the content is not blocked for all mobile users, but only a section of users. The screenshot below (on the left) shows the prompt that mobile users may get when they open a page in a mobile browser without being signed in. The first scenario happens on the desktop and the second exclusively on Reddit mobile at the time of writing.
Or the content may be blocked and you may get a prompt to either sign in to an account or use the official Reddit app to access the content. If you click on a link to Reddit, one of two things may happen: the actual page on Reddit may open right away and you may read the original post and the replies right away. It is not uncommon to find Reddit links in the results of Internet searches.