My step dad is 94 years old and insists on living alone, but it’s not safe. What do I do?

Because he seems to be in sound mind & that of an addict, I can only offer a conversation to have with him about his future. Is he paying his bills, seeing a doctor, dentist when needed or recommended? Does he have money set aside in case he has a catastrophic event that requires moving into AL or SNF? Has he appointed MPOA, POA, or had Advance Directives completed. He may be resistant to talk about this issues. Be there to offer an ear, but not finances or any abusive behavior from him. Because of his addiction & selfishness, he doesn't seem willing to get even a slight bit of assistance he needs. Keep in contact, but take care of yourself. Maybe he'll realize without your help, he will need to reach out for assist. Know that you've helped as much as he'll allow, but don't give too much of yourself. Read about APS in your area, but know that if you call them it might sever what relationship you have. It seems you are the closest person to him. If not maybe have a conversation with a closer relative to him about your concerns.

"Legal recourse" is not definitively connected with familial relationships. If he assigns someone as his PoA, that person does not have to be related to him. Anyone can pursue guardianship, but the court needs to sanction it. Are you his PoA? If he has never assigned anyone and refuses to do so, then you will need to do as Alva suggested: call APS when you see that he is in appalling conditions. Then the county will eventually get guardianship and they will control every decision. Not him, not you. Maybe if he knew this, he'd be more inclined to assign you as his PoA? It's worth one discussion with him, no more. If he waves you off, then you will be standing on the sidelines watching the train wreck unfold in slo-mo. This is just the reality when people don't plan and are in denial about what's happening in their lives.

Is he still driving?

I wish you peace in your heart that there's not much you can really do if he doesn't see the need to act.

If he is truly in his right mind, then there is little that anyone can do about this. It is unlikely that someone would have a guardian appointed, I think, if he is mentally capable of making his own decisions. Best you can do is what you are doing I think.
If you believe he is truly in danger then you can ask Adult Protective Services to check on him, his living conditions, and request their advice of how you should proceed.
This has to be such a worry for you. At this age, and with what he is doing to himself in these conditions it is truly self-limiting problem, because at some point they will not allow him discharged home. That may be now. Talk to them at his facility and tell them what you told us; tell them you feel his discharge home is an "unsafe discharge". Not a word they like.