Most online communities have a low barrier of entry and effectively no user onboarding, and end up becoming chaotic messes where content is difficult to navigate. Obviously this is fine for more chatty communities, but is unfortunate in more serious and discussion-focused forums and for content archives. Even on Lemmy, there are communities where formatting rules are completely ignored[1]. This results from a combination of site design, moderation, and user respect for the community (three things notoriously bad on reddit-like sites, and well, most popular sites)

A couple of exceptions to the trend are forums which enforce a barrier of entry and quality control (unfortunately I can't recall any right now, but I would love to hear of some!) and some booru IBs. A booru site is an archive where users upload media without titles and tag it for easy searching. If a booru manages to enforce a decent quality of tagging (and there are mechanical ways to assist with this, such as tag aliases) then the site becomes a well-organized online content community.

Most boorus I've found allow NSFW content, so here are some work-safe examples:

• FindAfox (photos and videos of foxes)
• FIRST Robotics Competition Archive (unofficial)
• Safebooru (mostly anime drawings)

Note: feel welcome to list slow or 'dead' sites!