My trick is, I cheat. I'm happily single, live alone and have no children. That gives me the luxury of doing the heavy lifting in my friendships. I travel a lot and most of those trips are to stay with friends in their homes or to meet them at a third destination. That's been the most effective way to stay very close to my friends, as well as to become close to their spouses and kids. I understand most people can't do this because of their own family obligations. But maybe it's something people with families could do just once or twice a year to visit people important to them?
Beyond that, I'm usually the one to start group chats or send memes on social media or schedule video chats. Sometimes it's a chore, but usually it's effortless for me. And the close friends I've maintained to this point are with people who are usually very eager and able to stay in touch on their end. The others have fell by the wayside over the years. And some I have consciously excluded from my life when I realized they were bad friends.
I'd also add that, as a man, I find that women make better friends then men, especially past our 20's, and I'd encourage all men to consider finding and building more non-romantic relationships with women.