I use Medium for this! 100% free, don’t have to paywall it, lovely and simple formatting, it actually can expose you to potential clients but you can also use it as a portfolio.

Medium is a great choice! I agree with @many-mechanic-52814! Also, I have a folder in my google drive that's specifically for my portfolio. This is for when I'm applying to positions that want to see things that are more demand-gen or other formats than blog posts. I keep content there from previous positions (as content gets updated, so something you wrote may not exist in the future). I suggest that as an easy, mostly free place for content that's not long-form.

I am also a new freelancer and I've had a great first few weeks. But if I didn't have my own blog to use as proof I know what I'm doing I wouldn't have any of the clients I've had so far. An effective way of getting clients and practice at the same time is to create an article that is exactly what you're applying for. You can do this in Google Docs. Now you have a portfolio piece and an exact match writing sample. Then create a portfolio in a well formatted Google sheet. Link out to all your different google doc samples from there. Easy to update. Easy to share. Completely free.