This is a really interesting read on what a writer who is actively hiring concept artists is looking for.
I will say it’s important to note that requirements for concept vary based on who is doing the hiring but there’s really good insight in here. https://twitter.com/lostagainb/status/1327197069552054278

The biggest thing missing in here is that some bigger studios have more granularity with concept, so some people are doing character, some are doing environment and people specialize. Polished art with character added for scale are sometimes environment concepts for lighting etc

But that’s case by case and you can easily get a sense of that by doing research on how the companies you’re applying for are structured

Overall this is exactly how I worked on the character concept team at ND and so far on the Wonderstorm as a more generalized concept artist. Our job is to showcase what this thing could look like in the end, to pull all the direction together so everyone can be on the same page