Building projects is definitely an excellent way to boost your skills! I'm going to shamelessly plug our site, https://www.frontendmentor.io/.

We handle the project ideas and designs, so you can focus on the coding. We try to make it as close to a real-world development workflow as possible. We've got five different difficulty levels and as you get to the Intermediate, Advanced, and Guru levels, there a many full-stack options, if that's something that interests you.

Hope you find something you like and best of luck!