From reading other answers it is clear this is a familiar situation to a lot of people, myself included. I'm in my 40s, and incredibly I still know people like this.
Some people are just late starters, often people that weren't "academically smart" so didn't do well in school but are still smart in other ways and eventually find their way.
Others though never change. Their thinking is just geared towards wallowing rather than doing anything about their problems. I think some believe their problems - their lack of a job, lack of money, lack of a driving licence - actually define them. And of course it is all cyclical - can't get a job because I don't have a car; can't afford a car because I don't have a job. It is frustrating to any rational person and I can understand why you find it toxic.
So - you are looking for a way to break contact rather than offer help. You probably imagine an offer of help will be tiring and strung out, which it may well be.
But why have a conversation with her at all? She complains to you that other friends have drifted away from her. If any of those other friends had actually had a conversation with her about severing ties you would surely have heard about it. So if they just faded away and ignored her, why do you feel the need to announce your departure? I can only imagine you do hope it will have some effect on her.
Honestly, if she is someone who enjoys talking about her woes then a conversation where you just attack her and then leave will just turn into her newest woe to talk about with the next person willing to listen.
If your mind is made up to break ties, just drift. It will hurt her less. Don't reply to emails, don't answer calls (or decreasingly answer them over time) and don't tell her you are coming to visit. If you are connected on social media then move her to a group that limits what she sees.
If you are to have a conversation with her then at least make it useful to her! Use the opportunity to encourage her, but show that you don't have the time or energies to carry her if she doesn't.
I feel the most useful conversation you could have (useful to you both) is one where you don't announce that the friendship is over, but show how her inaction in dealing with her problems is forcing the end of it. You're not closing the door on your friendship, but rather showing her the way forward and then closing the door on the way out. She can either follow your advice and keep up with you, or she will know the reason why your friendship ended.
I'm worried about you. You could fix a lot of the problems you talk about, like having no money or car, but you don't do anything about it. Everybody else has grown up, moved on, got jobs. There's nothing stopping you from doing the same.
And perhaps, after any response from her, go on to make your point:
I like my life now. I wish I could say I'll always have time for you, but I have to be honest, it is very draining when a friendship is one-sided. I can't always be the one to drive, I can't always be the one to pay for things. And I can't constantly listen to you talk about the same problems you could do something about. If you had a job and a car you could get out and visit people, enjoy your life, and have new things to talk about other than having no car or money.