Is it possible to make money using your Linux knowledge if you're not a developer? I know I can become a professional devops or sysadmin if I take some courses and master advanced networking. But is there something I can do now as an average, moderately experienced linux user?
I did nearly a decade. DE's (or just wms) on devs' desktops and obviously ssh or console shells on server and network hw. Devs may or may not take care of their own software, though.
Also network protocols, sniffers, support, hardware, security... It tends to expand and admins are the goto for tech questions. So it's kind of a know everything about everything job. And a very thankless one, since if you do your work right, nobody will even notice what's going on since everything just works.
I worked in a small team and our stuff rarely broke. We set it all up to use minimal resources and mostly automated maintenance and we went unnoticed for most of my time there. Everyone else thought we were just sitting around doing nothing and getting paid for it. It created an uncomfortable environment, was glad to leave at the end of it.
I think the internet can inflate this view. In my experience supporting devs, there are many very smart people in their wheelhouse who are not very good at system administration. I think it is much like academics who are also often assumed to be good at computers, rather than good at what they do on computers.