How to make friends as an adult?

As an adult, I find that I struggle to make new friends. I want to continue to nurture my current friendships, but I’d love to have more friends and more connectivity in my life. How do you do this in your 40s? It seems like so many people already have their lives/friends set in place.
I work from home much of the time, so I’m not even sure where to meet new people.
How can I have more friends?