Freewriting is a process in which you write without stopping for a set period of time. It’s the main mechanism behind “morning pages” popularized by Julia Cameron in The Artist’s Way. Tim Ferriss mentioned morning pages and the aforementioned book in his YouTube video titled “How to Use Writing to Sharpen Your Thinking”.
Oliver Burkeman wrote about it recently in his newsletter, The Imperfectionist. He recommends starting with 10 minutes. You don’t have to write particularly fast. The idea is that you write with an uninhibited mindset. What comes out might suck, and it will suck most of the time, but occasionally you’ll get some interesting insights and you’ll be able to get to the bottom of your thinking. The thinking behind your thinking, perhaps. I think he used the phrase “drain the faucet,” although Ali Abdaal may have written that in his newsletter about the same topic.
Another idea is that it doesn’t matter that what comes out sucks. It’s better to take imperfect action than no action at all.