Find a company that works with open source projects, and contribute to them on your own time. Bonus points if you actually use them for your own projects so you

Find a company that works with open source projects, and contribute to them on your own time. Bonus points if you actually use them for your own projects so you are able to provide real-world use cases and feedback to them. This especially helps if the company is a startup, in which case they most likely are understaffed to keep everything up to date and bug-free. They will also be more likely to respond to your feedback in an actionable way besides a "thank you" from a maintainer.