I don't think it's you. Most of my friends, all mid 30s or so, have the same issue.
Now granted a few are single mums so will find it harder anyway, but the others are also struggling.
Of the two guys I am reasonably friendly with, one 29 the other 34, both have said they will never marry or have kids. Their reason seems to be mainly that they just don't need the "grief" and that they don't need a woman for anything so what was the point.
They can have sex whenever they want with women from dating apps and see no benefit in anything long term.
I think there has been a cultural shift in men that we havent noticed. We still want to settle down, have a family and raise children. Guys these days just dont. I think it will only get harder as time goes by. Men and women just want different things I think. You can say they're all immature and need to grow up, but it's all irrelevant when they won't have kids with us.
I guess you have to work on your "game". You need to stand out from all the other women they have to choose from. Ask yourself why they would choose you over the other woman. Mostly though, they just seem to go for the pretty ones. Which for most of us is something we hate, but we have to try to compete if we want a man.
Not sure what the solution is. Maybe we have to find a way of being "useful". Not sure how that would work. Kids was the one thing we could provide a man, but now they don't want that. Leaves us in a sort of limbo. Not sure we ended up here. Even the girls in the office where I work "joke" that none of the guys ever try it on with them. It's like they have become invisible.
We are living in steange times.