Yes, even if you're not fond of being on camera, you can be a Developer Advocate! It largely depends on how DevRel is run at the company. There are often sub-teams inside Developer Relations / Developer Experience that aren't public-facing, but still do important work.
For example, Netlify's Developer Experience team has an Integrations Engineering team and Documentation team that do similar work as a Developer Advocate at other companies, but they don't need to be working public-facing.
I can't speak to Auth0, but I can speak to Vercel! At our current stage (there's four Developer Advocates on my team), they're all involved in some form of public advocacy and helping our customers succeed through content creation and our communities. In the future, we might have entirely non-public roles on our team.