It took me about a year to earn a full-time income as a writer, but I also didn't take it as seriously as I should starting out.
That was over 7 years ago, and things are much different now. I started out writing on a few platforms and it eventually lead to long-term clients.
I also used to publish on Constant Content and I would make a few sales each month, but that website isn't nearly as popular now due to AI.
If you want to make it as a full-time writer now, you can use Medium as your portfolio and reach out to marketing agencies or any companies looking for writers on LinkedIn.
Working with an agency can give you experience and you will often cover a variety of topics. All of my work now is with agencies and I still make a few random sales on Constant Content.
I also earn money here on Medium, but it takes a while to get established.