I've changed domain few times(Physics tutor to Yoga therapist and then coming to data science, developing product/team lead). Currently I'm focussing on multiple freelancing. I was able to do it through networking, find opportunities.
It's doable but you need to go through unconventional ways of searching opportunities. With AI, market is changing and people who know multiple things are welcome but at the same time, a lot of companies focus on hiring expert in one domain. If you love it, you will surely find opportunities. Stay positive.
Your particular case is very uphill - there aren't that many people or companies that do this, very limited number of openings, you have no relevant experience, not in the pipeline for internships. Learning about databases and doing a bit of C++ and Rust is worth just about nothing in terms of helping you for these jobs.
Keep it up as a hobby, find open source projects in which you can make meaningful contributions (that alone can be very hard), spend years in it, then maybe you'll have a better shot - whether all of that's worth it is for you to decide.
If I were you, I'd reconsider why you even want this in the first place.
Get yourself a time machine and go back 10 or so years when the market was hot enough for this it be feasible.
Your best chance would be to apply for an SRE role. Even in there there won’t be much database development, but more of maintenance and scaling where your deep understanding on DB might be helpful. Once you have more exposure and experience, then you might be able to apply directly for a company that develop DBs