This is more or less the advice that I was going to give. I would add on to it by recommending that, if you don't know what to build, go find an open source project with open pull requests and start fixing broken things. Keep track of your submissions and use them to start creating a portfolio of the professional work that you've done this way a gratis.

In addition to doing volunteer work this way, also look for various "bug bounty" situations for accumulating similar "professional micro-experiences" that you can also use to show that you have been crafting and delivering functional code into one or more projects.