It’s a bit redundant since the O stands for “Optimization”, but it means Search Engine Optimization. Basically structure your stuff so it shows up in more searches (use popular terms in your profile, make posts with key phrases, fill out all the fields).

I’d say all of the ones I’ve bothered to try work? Some of them have annoyingly low pressure, where I’m almost kissing the spigot, but none have been undrinkable.

You could self-host GitLab, though if you’re looking for exposure it’s probably not the best.