My point is that an alien civilization maybe has thousands of years (or more) of technological advantage to us. They‘d have things, we currently couldn‘t assemble. If we had the technology and could study it, sure, that‘s different. And again, we already have theories how intergalactic space travel could work (e.g. worm holes), so there is definitely a possibility that an advanced civilization already did this. I don‘t think they visited earth though, but still.

Edit: Btw, also maybe an alien civilizations has completely different or new resources, we haven‘t even discovered yet.