Does a BA need any Domain Expertise?
Domain Expertise is something a person gains from working in one particular domain for more than 10 years in varied positions and in varied departments. Domain Expert will be expected to have complete knowledge of that particular domain from top most level to bottom most level - horizontally as well as vertically.
If you fall under the above criteria - then you can apply for an SME job.
If you do not fall under the above criteria - then you can apply for a BA job.
If you have anything less than 10 years of experience after your last education, then you do not need to think about domain expertise.
Remember, domain expertise cannot be learnt by reading a book or taking lessons from someone or watching YouTube videos or searching online. It must come from your own experience and that only counts when you go to the interview. Everything else is just a simple myth.