This may be an instance-specific problem because I’ve had no problem editing posts on other instances. When I try to exit the title and body of this post, I click save (or whatever) and without error it behaves as if my change was accepted.
Most instances take a minute or two to re-render the screen to show my updates. If the wait is long, I sometimes do a hard refresh to make sure the change got accepted (and if I don’t do that and I do another update, the old content populates the form and causes the recent edit to be lost).
Anyway, with infosec.pub my edits on the above-mentioned post just take no effect, confirmed by a hard-refresh showing no change.