It isn’t difficult to start an open source project. Your project doesn’t need to be another Linux; find a tool that you wish existed and make it. Create a focused and stable open source project you can talk about well and you will impress your next interviewer.
Recruiters love engineers who have started their own open source projects. An developer who starts a project from scratch shows that they are motivate and organized.
Working on an open source project with other people gives you an opportunity to show you can be a productive member of a community. It will also make you a better developer. Putting your code out for other people to see will make you more careful with what you write and having peer reviews will help you increase your skills. And it builds your brand.