OP yes most people are in relationships, or at least that’s the goal for most young people.
And nearly everyone I know is in a long term relationship or marriage with kids. Those of us with decent (not perfect) long marriages whose kids have left home and we are getting on ok, don’t post on MN complaining about our menfolk. In my anecdotal experience we are the majority.
So I completely understand your sense of isolation. Both from being single (I get the impression you would like a partner) but also from not knowing anyone in your position. It must feel quite lonely.
But I am sure most of us know at least one single woman. One of my close friends is almost 60 and single. Had a few flings. Never anything serious and no kids. She is a university professor, travels the world and has a very close relationship with her nephews and nieces. She would quite like a partner but it in no way defines her. And there is so much that’s good in her life.
None of us is leading a perfect life. But it’s hard when things don’t work out as planned. I guess all I can say is that there are definitely single women out there who are fulfilled and content. Even the ones who would quite like to have a partner.
I think the yearning for kids is something different. And experienced by women in relationships too.
I hope you find contentment OP. Your feelings are valid.