Following changes to its API access, users are forced to log in on the official Reddit app if they want to view NSFW content on mobile.
I’d recommend setting one’s own browser to automatically redirect to old.reddit.com for the occasion they might need to find that rare technical solution/see sum tiddies.
I use this plugin to fetch the last known stored version of a given page in the Wayback Machine: https://addons.mozilla.org/en-US/firefox/addon/reddit-to-wayback-machine/
Really handy to get a read-only version of useful threads that have been since removed in protest or put in a private subreddit. Plus it doesn’t give them any traffic, as it uses an external proxy.