As someone in this group, I think there are a surprising number of middle aged people without any friends. If you move or lose your friend group (or never had one) it seems harder than ever to find friends.
Acquaintances, though, I have many. Many of I talk to regularly, but would never consider them a friend, because well, I know almost nothing personal about them. A former boss that I meet up with anytime we are in the same city for dinner and drinks, I've known for nearly 20 years, but I don't know his wife's name, I know he has 4 kids, and I've met them all in passing, but no clue what their names are, etc.
Maybe I'm weird, and maybe I'm a bit lonely, and maybe it has taken a couple decades to realize I squandered all of my in-build friends from childhood, but I'm not sure I'd do it differently. I've had a semi-successful life, and most of my high school friends still live in their hometown, have dead-end manual labor jobs, or have died/disappeared from drug use.
Therapy tells me I pre-reject friendship so friendship doesn't reject me, and I agree with it, but don't feel like changing the pattern.
LOL that would describe me perfectly as well I think. I have not had "close" friends since I was in my early 20s. Then everyone moved away and we all started our separate lives.
The next group of friends came along when I had kids, and parents naturally became friendly because we would see each other at kids activities, sports, etc.
Then the kids grew up, and there was nothing bringing that group of people together anymore. I still see and talk to one or two of them but it's pretty infrequent.
Now, the idea of maintaining a real, close friendship just sounds like too much work. I'm happy enough just living my life on my terms.
Most friendships are just formed of the people we see regularly due to circumstance. They may be pleasant but they are not deep, and they will fall apart as soon as circumstances change.
Its not great but also not a huge problem - I believe now I have some amount of Schizotypal personality spectrum, and have all my life, though I never admit that to most people IRL since the label freaks people out.
In other words, friends won't drop into your lap. You have to go where fish are actually biting and cast out your line.