Saviour Akpanukoh
Ayye friend, this is a hard question because it is still very blurry!
Even though groups like opensourcedesign.net have been around for 5+ years and years before that, designers were always interested in technology and especially technology that empowers people freely there are still structural reasons open source design contributions are low and difficult...but we are making our path stronger each day!
I started writing a guide for this here on my Notion: notion.so/erioldoesdesign/Guide-to-getting-involv…
But there is lots missing. The best thing you can do as a start is to find other open source designer peers to lean on, build networks and discuss open source and design. You'll find those in the open source design forum: discourse.opensourcedesign.net
The frustrating part is the ground level work is more about helping the OSS projects, maintainers and developers understand what design is capable of offering their OSS and how to ask. It'll be more conversations, discovery and coaching at first (and also documentation writing!) but you'll also find some OSS project more than ready to receive design help across the spectrum of design from UX research to graphic design to usability testing!