Look up “developer relations”. It’s kind of being an advocate for the software made by a company. Part of that job is to have respect so open source advocacy goes with it. Double goes with it if the software made by the company is open source.

This is the closest job that I could think of to an open source advocate.

I believe organizations like the FSF, FSFE and SF Conservancy employ basically lobbyists to help represent open-source.

And organizations like Mozilla, KDE, GNOME, openSUSE, The Document Foundation, Wikimedia etc. will have basically open-source community managers. So, where you could potentially help to steer an open-source community, as far as that’s possible.

But yeah, these positions are extremely rare. Like, we’re talking a few dozens on the whole planet.
People in these positions usually have made a name for themselves in other ways and have experience in similar jobs…

Yes. However, such positions are not common, because they rely on a pre-allocated pile of money being dedicated towards FLOSS.

When I was at Oregon State University, I worked for the Open Source Lab; you may recognize them as an option on your distro’s mirror list. During part of that time, I worked for the Open Source Education Lab, an outreach program which was funded by a grant through the College of Electrical Engineering and Computer Science (now the College of Electrical & Computer Engineering). This grant funded some get-togethers on campus, the local Linux Users Group, and some one-off interactions like giving talks to undergraduate classes about how to use FLOSS software.

But, when the grant ended, so did OSEL. OSL and the LUG are still around because their funding comes from OSL tenants and LUG club members respectively, but they are not focused on outreach and advocacy.

Get a benefactor (or many) to form a foundation that pays for such advocacy or find existing foundations that fund advocates.