Wow these comments are depressing, so many people struggling with Substack.
The article is true, but not the full story.
You do need to offer your readers something of value to make money with Substack, but it is absolutely 100% possible to make a decent side hustle income with it.
I have two Substack publications, one just passed annual revenue of $21K (from zero subscribers) and the other is free to subscribe but makes money through coaching services and digital products.
It's definitely not an easy road, and the thing that most creators from Medium struggle with is that you have to find a way to get your work in front of new people every week if you want to grow (Medium does that for you automatically).
Then, when new people see your posts you need to convince them to become (free) subscribers, and then you need to convert a few of them to paid subscribers.
If all that sounds too hard you should definitely stay away from Substack.
If you're up for the challenge, and want to tap into some of the financial rewards others are getting, check out some of my posts on Medium about Substack and discover it's possible and actually quite fun.