One perspective that might be helpful is that humans have for many millennia pondered this question, so it isn't new.
We have a more exacting (but not perfect) definition from a biological perspective. We also have philosophical theories about personhood[1] and mind[2]. One can hypothesized that these, and other characteristics, such as the emergence of culture, etc. also exist in other entities (whether on earth, alien, or technology like AI), so perhaps humans can be though of us as occupying a region across these different dimensions that represent a unique combination. But we don't have exclusivity over a particular dimension (like reasoning, for example).
Another perspective that might be helpful is that even if there are other entities that are very much like humans, it does not take away YOUR and MY experience of being human or the value and joy we derive from it. If anything, it can help us understand ourselves better. This introspection ability is another one of those characteristics that humans have.
[1] https://plato.stanford.edu/entries/identity-personal/
[2] https://plato.stanford.edu/search/searcher.py?query=mind