In my experience (40 years in software dev) “domain expertise” refers to business domains, not programming languages or frameworks. For example I have significa

In my experience (40 years in software dev) “domain expertise” refers to business domains, not programming languages or frameworks. For example I have significant domain expertise in enterprise logistics. I have significant technical expertise with relational databases. Either or both of those let me offer value to potential employers. Domain expertise may refer to security or scaling infrastructure, but unless you write compilers and libraries it usually doesn’t refer to languages and tools. React/redux doesn’t count as a domain, nor as a technical skill that takes so much time to master that experts have 10x the productivity of average developers. And it’s likely to fade away fairly fast, compared to something like Oracle or web development at scale. No one “becomes” a specialist, that’s not an identity. It’s a shorthand to mean someone with extensive and uncommon experience and expertise. You gain domain expertise by working in a domain long enough to know what you’re talking about and demonstrating you can add more value faster than most other people.