I'm not a Linux admin, but I think there are certifications you can get and exams you can take to show you understand stuff about shell scripting and related topics, if that's what you're interested in.
I think they have questions like "Make it so a welcome message and the time display when someone logs into your Linux server", among other, harder things.
I don't know a huge amount about the job market, but just saying you have those kinds of skills on your CV along with a bit of experience in some other tech/coding/data stuff might even be enough.
Been using Linux for 25 years so i don't know if it's comparable to today but ironically it was setting up game servers for fun. Then i applied for a game sever hosting provider. i think they have mostly died out now. Then just kinda jumped over to web hosting this was before cloud was a thing. Then kinda moved into internal IT running corporate IT. The nice thing being 100% Linux admin i don't have to mess with AD and FSMO. Even though I know how to i keep quiet about that.