A lot of great suggestions in this thread. To add to those, I want to talk a bit about how to form a strategy that will help you achieve these goals.

First, not every world problem is solvable with design. Being aware that you are one facet of the solution is both comforting and overwhelming. To have broad impact you often need a team of experts to cover the pipeline from end-to-end, so that means things like solving for the terrible Heath Care experience in the US or UK require massive reformations in how that industry has been run for almost 100 years. On the bright side, there are lots of private clinics aiming to solve this - One Medical is a great example (I promise I dont work for them, just a fan of their approach). If you have the motivation to aim for this level of impact that is awesome, but most likely wont be available to you until you have several years of experience under your belt and area ready to move beyond graphic design and into a role as creative director (like Jony Ive for example).

The good news? You can start planning for that career path today. Start small by targeting industries that you already have experience with, even if that experience is indirect. Got a passion for food culture? Maybe run with that. Seek out reputable companies that are trying to perfect food distribution to restaurants and grocery stores. From there you will start to see the pain points that cause issues like food deserts in inner city areas. Start to slowly invest time on the side volunteering with non-profits and groups that are actively trying to solve for these oversights in the food distribution system. See whats holding them back from making big changes. Regardless of what industry you focus on, assume you will always be spending time on the side volunteering with activist/non-profit groups that are already targeting the crisis at hand.

Your journey now is to marry your charitable 'side-job' with your full-time job, and your choices will hinge on reducing the gulf between the two. One day, they can be one and the same job - and youll see the path towards that goal unfold for you as you roadmap your steps to achieve that goal. Sometimes this means creating your own company - but it certainly doesnt have to be that way. Lots and lots of private companies are stepping up to offer people another option than the current, broken norm, such as One Medical that I mentioned above.

Lastly, Ill echo what others have said about donating your earnings. Ill take that a step further and suggest the idea of working a charity initiative into your regular earnings model. If you are working for yourself - this is a great opportunity to build your passion for giving into your pricing. I love seeing places that actively advertise how much they donate and incorporate a breakdown of that cost into their payment model. The invoices they provide will outline exactly how much of your payment is donated and to what organization. By doing this, these companies are not only making a positive impact, but they are fostering a culture within their industry that values giving-back. Often clients will seek them out specifically because they want to support a company that values altruism and sees it as a sustainable business model.

Sorry for the novel-length post! Ill close with this: just remember - always ask yourself what you can do TODAY, however small it may seem. You may not be Elon Musk, but the path to that kind of impact is created step-by-step with every small interaction. Every relevant experience is a learning experience. Volunteer, find an open-source project, talk to others who are trying to solve problems too, and network with like-minded people. We all start out as little cogs in a big machine, but together we can change the system, one step at a time.