I used to think this, but I no longer do. I'm also mid 40s. People say that religion gives them meaning, but I think what it really gives them is
community. Especially with the pandemic, all of the "automatic" ways that we used to run into friends and acquaintances have dried up. It takes much more active effort now.
While I'm surely projecting on to OP, I think it is very common for very career or goal-focused folks to have good but perhaps not overwhelming success, then hit their mid-40s and think "Umm, what do I do now?" This can be especially common for folks that perhaps sacrificed some of their personal relationships in pursuit of their goals.
I was very lucky in that I had a fantastic therapist who really helped me understand the roots of my depression. Even then, though, after a while insight can only go so far. It's very clear to me that I've neglected nurturing my friendships and relationships, and I think there are likely others out there in a similar predicament, especially on a place like HN. I've actually started to search for a life coach that can really assist with the tactical side of nurturing friendships. That was a big missing piece from my therapy, which was otherwise great.
On one hand it's kind of embarrassing to feel like I need to pay someone to say "Yes, it's been a while, you should call Jane", and "Did you mail your Christmas cards?", and "Did you send a thank you note to Bob?", and "Why don't you invite the Jones over for dinner?", but I've come to see it like a personal trainer. Most people know the basics of working out, but they need to pay someone to actually get them to exercise. On the friendship topic, for some folks this sort of "social knowledge" comes naturally - I've come to easily accept it's not natural for me and I need some assistance.
As far as I've seen from studies of happiness, basically it all comes down to "love", it all its different forms. Modern society makes it much more difficult to build a true sense of community and friendships. I think we all just need to spend the effort to find it without some of the "default" structures that used to exist in the past.