Sometime ago, I considered applying for Technical Writing roles so I could have a lucrative side job while I work on completing my PhD. I applied for several jobs but did not obtain a position. I am very surprised by the number of people who are either already in a Technical Writer role or seeking to obtain a Technical Writer position. Apparently, even software developers are looking to move into the Technical Writer role. There is a lot of competition.
In addition to writing/drafting reports as a Financial Auditor at ODCA in DC, I wrote requirements for the design and development of information systems. At one important job, I got lots of practice writing use cases and requirements statements ("The system shall" statements). Requirements are "published" in a system requirements document. The document is usually circulated internally.
Did you see my work on the requirements for a new system to assist with job search/hunting? It is available here: https://fahmeenaodetta.blogspot.com/2022/12/job-search-system.html.
I also wrote an article on requirements and data quality. See it here: https://www.modernanalyst.com/Resources/Articles/tabid/115/ID/2981/Improving-Data-Quality-User-Interface-Design-and-Functional-Requirements.aspx.
I first learned how to write use cases and non-functional requirements during a training program at a particular company. (There were all sorts of issues). I improved my skill at UMBC.