You get in contact with the current maintainers and talk to them. Real human communication is the only shibboleth that will survive the AI winter. Those soft skills muscles are about to get a workout. Tell them about what you use the software for and what kinds of improvements you want to make and how involved you'd like your role to be. Then you'll either be invited to open PRs as a well-known contributor or become a candidate for maintainership.

Github issues/prs are effectively a public forum for a software project where the maintainers play moderator and that forum is now overrun with trolls and bots filling it with spam. Closing up that means of contributing is going to be the rational response for a lot of projects. Even more will be shunted to semi-private communities like Discord/Matrix/IRC/Email lists.