Does observation alter an event?
I understand that some people have the interpretation of quantum mechanics that FOS described, and I’m not one of those. From my understanding, an observation doesn’t alter an event in and of itself, and nor can an observer be totally isolated from an event. So being an observer, is being part of the system, and will have influences on the system (whatever system one is observing). Such influence may be minor, and it may be significant.
So from my perspective, strictly speaking, alter the event, no; alter the system within which the event occurred, yes.