I think when you look at this it makes more sense if you think of it as a hobby outlay, rather than looking at the specifics of the hobby. If E&P is your only hobby and you spend a lot of hours on it every week, and it brings you joy/solace/comfort/companionship or helps to make covid a bit more bearable or even just effectively kills boredom then I would say its quite reasonable to spend $100/month on it. I mean if you compare that to going out and getting drunk frequently, it is cheaper than that and arguably better for you. Or you could race cars for a hobby which would run you into the thousands.
If you casually play a bunch of mobile games and you spend $100/month on each then that seems less reasonable to me as it becomes less about a dedicated hobby that you invest in (invest meaning money going in, fun coming out). Although if you have that kind of disposable cash lying around then it is entirely your perogative to spend it however you want to.
A fine line that everyone has to walk in all of this is that the money you spend should not be regretted, regardless of what actual outcomes you get out of spending that money. If you regret, then you are spending more than you should