I also see myself as a software engineer first but with a keen interest on these topics. I found a good place calling myself UX Engineer; basically frontend engineering with close ties to design and product teams.

Maybe get more into HCI research? It's basically computer science + psychology. I actually used self-determination theory for a research project back when I was doing my CS master: https://dl.acm.org/doi/10.1145/3274329

HCI research also extends nicely into UX research. You could look for UX Researcher roles, but that'd be non-engineering. That's why I like "UX Engineer" as a title for people like us.