Every friendship is different. I have some friends that I only see a couple times a year, but we text every day. Inviting him out once a month isn’t excessive at all. Since you’re still having other positive interactions, I would just continue inviting him to low pressure things.
Inviting him to group events might be good, too. For example, “I’m going to be hanging out at this place at this time with these people if you want to join.”
They added spoilers, but they don’t work on the boost app or some others.