If "we were the only" is true so is "we were the first" ...

However, there exists or has existed one planet with the first civilization ever.

It is also stupendously implausible that our civilization arrives at all in a mere 14 billion years, considered against the gazillions of years in the potentially infinite lifespan of the Universe. Yet here we are.

If it is difficult for civilizations to develop, then our existence is so implausible already that being the first is not such a leap.

I did not imply at any point that we were the first, or only. Perhaps in our galaxy. I don't know if we could ever find out about civilizations in other galaxies.

There are a 100 billion galaxies. I'm ready to guess each has at least a few planets theoretically capable to sustain life for long enough.