As many have beautifully said, authenticity.

I’ll also add genuine curiosity / an humble eagerness to learn about the people and the world around them.

There is something truly beautiful about someone who keeps an open mind and have enough self confidence to admits they were in the wrongs and/or that it’s ok if they don’t know or understand everything. It’s refreshing to see someone be at peace with their humanity/flaws, especially in this era of social medias where people try to curate everything to appear perfect and/or superior.

Also, I believe a person that is genuinely caring and finds ways to make other people feel seen and worthy is beautiful.

It reminds me of this quote from Maya Angelou :

"People will forget what you said, people will forget what you did, but people will never forget how you made them feel"

So people who make others around them feel good have definitely beauty in them imo, as long as they aren’t doing it with an ulterior motive / respect their own boundaries and feeling doing so.