What kind of things do you like to do? Join a club, or team. Or whats something you think you might like to do? Take group lessons, or join a club and admit you know nothing and want to learn. People love sharing their hobbies. Mahjong, tennis, book club, home brewing, hiking, knitting, bird watching, ball room dancing… anything. Hang out in the organized setting multiple times, then if something clicks, hang out outside of the group. "Hey we should play mahjong at my place. Know another 2 people who we could play with? " “that was a great hike. Im hungry. Anyone want to get lunch?”
Take initiative, but dont force it.
You say that, but my wife and i have done most of the things i listed above and made friends this year. We joined a gym that had tennis group lessons and now we meet just with people to work out, i joined a soccer team and now have been meeting up with folks for watching world cup games. My wife joined a mahjong class and now has regular games together with her class mates even though theyre not in class any more. She joined a book club that gets together once a month. My brother decided he wanted to get in shape so joined a triathlon club and completely changed his way of life and now travels the world with his new friends.
Either youre being disingenuous or you havent actually tried these things
For reference, we’re almost 40.