It seems editing is disabled after a period of time. I see no reason why it should be so. Please consider removing the time limit, or if that’s not possible technically, extend it to the maximal value possible.
For example, I tried to fix an old typo and had to add a reply instead.
I can see this being a problem if we are to consider the forum as a reliable source of information. Imagine if someone were to edit their post two months later, when their post was already linked to from various sources, to completely change what it says. That could, in theory, be a problem.
One counter-argument is that moderators can reverse an edit, but it can be hard to track unexpected edits anywhere across the forum. (Maybe Discourse has a feature to detect that, but I don’t know.)
Regardless, extending the time limit is probably fine (just maybe not removing it entirely).
For the time being, I can see it being totally valid to ask a moderator to edit your post to make a minor change (at least, I guess it’s easier than the opposite: reporting bad edits to moderators).
I see your point, but I don’t think in practice people here will abuse the edit function like this (and in any case edits are versioned). Perhaps I’m just not exposed to the Dark Side of the Forum… 
“In practice, people…” is a wild hypothesis to make on the internet (and irl)
The key word is here (preceded by the words you quoted): from what I’ve seen here, in this niche technical forum, it’s hard for me to imagine misuse of the edit function. If people want to misguide or do any other malicious activity there are other ways to do that. When considering the pros and cons of editing I think the pros win.
One scenario where not being able to edit causes misguiding is when Typst itself (or its ecosystem) changes in a way that makes a selected answer outdated; not being able to update the answer fossilises it in an currently-incorrect state.