Very interesting. How did you find projects to contribute to in GitHub for documentation editing? I've always wanted to do this kind of work but haven't been able to find opportunities in it.
For GitHub, I looked at projects that interested me, but not necessarily having the skills to contribute code. So I would pour through the docs and find errors, typos, mistakes. These kinds of things. Cleaning up. Sometimes added documentation that was missing.
https://www.indeed.com/q-Technical-Writer-Editor-jobs.html
https://www.flexjobs.com/jobs/technical-writing
https://www.upwork.com/freelance-jobs/technical-editing/
https://www.fiverr.com/search/gigs?query=writing%2Bproof%2Br...
You can also contact agencies like Toptal and Robert Half.
If you want a different type of job then you need to have evidence or a convincing story that you have literally done that job before, either as an intern or through training/education or as projects on your own. But the fact that you have literally done proofreading and documentation editing in a technical context and there is a record on Github seems to be concrete proof that should be possible to leverage into getting paid work doing the same thing.