So. I hopefully won't do much on this because, as much as I love ARGs and I love the lore implications, an arg on top of everything is way too much for me to handle theorizing actively on.
So I'll probably put my two cents in occasionally, but not often.
So here's my main theory for now.
"a lot of you are wrong".
To me, my first thought was "what if it's what I've seen everyone think?"
The author/s of the note.
I've seen a lot of people on how many different people wrote on that note.
So what if it's not different people?
What if it's just ranboo looking into his enderwalking state when he's awake, figuring out something bad that makes him think he needs to stop it "do not let this happen multiple times", then, as he drifts into a middle stage (like we saw how he was slightly aware when he went to the disc confrontation scene) because of the stress the realisation has caused, he's conflicted ("good but depends on what has experienced" "could bee harmful"), and when he finally goes into the enderwalking state, it's trying to help him stay enderwalking. It's forcing him to stay in that state "don't figure out how to stop it".
The change in pen textures and fonts could be the different states conflicting with each other and/or forgetting where the original pens were when adding to the paper.
Any outside influence would surely replace the paper, but ranboo, in that state of panic and stress would either forget where the pens and paper are, "effects: memory", or just not care to change it.
I don't know. I doubt its true. But yeah. Just a thought.
It certainly is interesting, though.
Also. More than one person who can enderwalk, "as those who have experienced it"? We know the person writing is Ranboo, "do you not remember doomsday". Unless someone else in the dsmp at that point could also enderwalk and ranboo and them met.
If it was just ranboo, it would have probably been like "when we've walked before, it has shown it could be harmful".
Also, what time-frame is this in?
Future? Present? Past? And how far into those if not the present?