The Solana developer develops the Back End, i.e Solana Programs that interact with the Solana Blockchain. To be a Solana developer you need to be familiar with Rust, Solana / Anchor, Typescript, and Solana web3.js. A general understanding of how blockchains work, and how the Solana Blockchain architecture works, is highly recommended.
You will be writing Solana Programs in the Rust programming language that not only interact with the Solana Blockchain, but also expose APIs for the Front End to call.
Solana developers typically work with Front End developers to build a full application.
Most say that becoming a Solana Developer is more challenging than becoming a Front End developer. There is some truth to that. Solana Development is relatively new, therefore does not have the same level of abundance of beginner friendly learning resources as compared to resources for Front End developer topics, although this is rapidly changing. The other challenge in being new, is that Solana developers often rely on tools and code libraries that are frequently updated (e.g by the Solana team themselves). Lastly, the topic of Blockchain by itself, is a relatively new concept and may even be challenging to understand for some experienced developers. But anything that presents itself as a greater challenge, often comes with greater rewards.