Looking for great project with desired stack

Not sure I could make my title more vague. I’m a Java developer, that reallllly would like to expand my tech stack, write and deploy an application. I’m thinking either a decent web app, or perhaps a Mobil app, for the HOA, start small with deliverable documents, authentication, push notifications, and simple chat rooms. My goal is to challenge my self over a long term project, and become proficient enough in a newer stack that would make me more desired in my industry. Initially I was looking at learning some react, a Cloud based DB solution, and possibly more. Suggestions for stacks, or items I could use to make my self more valuable would greatly appreciated!