FRF: food, recreation, fitness (and maybe volunteering which could in a sense be seen as recreation) will do it. I try to combine two of any of the above in a single day’s worth of proposed events, like a hike and then lunch, etc.
It’s not easy. You have to be really dedicated to keeping friendships alive by pinging every 2-3 weeks (monthly is probably just a little bit too long). Then see how often they do so with you over time, or how they attempt to carry conversations after initiation. Back away from the ones who just do not reciprocate, for one reason or another (and know that it’s not a reflection of you!). You may face many, many cancellations or outright rejections or possibly standups. It’s a marathon, not a sprint.
Are you trying to avoid some kind of account-flagging or something?