My favorite impact that I've had on my organization was the "no agenda, no meeting". It became a meme, minutes before the agenda-less meeting was supposed to take place someone would send it to a meeting chat or email, usually followed with ":)", especially if I were one of the attendees. In the rare cases I forgot to follow my own stubborn rule then it was a whole show, in hindsight, probably should've broken it at least once a quarter along with some penance to really help cement it.

However, I managed to "bully" everyone into following this simple rule because I had some influence in the organization; I was a manager of a large department. Unfortunately, interns will probably get an eye-roll for such suggestions, even if they reference their superior's rule.

My point is, don't send you colleagues this link, you will come off as rude. You'll get further by e.g. feigning surprise to the lack of agenda, and maybe you get to use that opportunity to spark a conversation about the importance of an agenda. If you're a manager and above, then by all means, use your influence to force it, it will make everyone's job easier in the long run.

Oh, as for the messages that contain only "hello", just ignore them, they will either solve their own problem or quickly jump to the point once they tire of waiting for your equally pointless response. Or just have a chat with your colleagues every once in a while, maybe they genuinely care about you and your cat.