The biggest thing I’ve noticed is not having a large community to feel a part of. Those I know who are active in church communities tend to have a more active social life. I have close friends for sure, but I do miss that sense of greater community and cause.
The only other thing I feel acutely is the sense of being all on my own and the decider of my own destiny. There’s no leaning on faith as a crutch during tough times.
This is literally the only thing I miss, having gone from very religious to very not. There just aren't really comparable alternatives that make socializing so easy.