Back when Twitter threads didn't suck (they could be viewed by people without Twitter accounts) I'd use those - tweet a description of my project with a link, then follow it with a few photos and screenshots.
These days I use my blog, with my "projects" tag: https://simonwillison.net/tags/projects/
I blog all sorts of other stuff, but if I was ever to trim back the one thing I'd keep doing is projects. If you make a thing, write about that thing. I wrote more about that here: https://simonwillison.net/2022/Nov/6/what-to-blog-about/#pro...
Projects with a GitHub repository make this even easier: describe the project in the README and drop in a few screenshots - that's all you need.
(Screenshots are important though, they're the ultimate defense against bitrot.)
I have many projects from earlier in my career that I never documented or captured in screenshot form and I deeply regret it.