I don't believe in UFOs. But if I had to believe in UFOs, this would be my position:
We have had modern humans for 500 000 years [1]. If it takes 10 000 years to make it from stone age to space age, we have theoretically had time to make that 50 times over. Maybe there was a previous version of a human civilization [2], then wiped out by ice ages or something, but a small number of highly advanced humans have survived and keep hiding from us. I think this could be somewhat more plausible than interstellar travel.
[1] Or maybe 1 million https://news.ycombinator.com/item?id=45510582