I often see university EAs aiming to do research projects to test their fit for specific cause areas. I don't think this is a good idea.
I think if you felt you were good or bad fit for a research project, either you were a good or bad fit for research generally or a specific style of research (qualitative, quantitative, philosophical, primary, secondary, wet-lab, programming, focus groups, interviews, questionnaires, clinical trials).
For example, it seems very unlikely to me that someone who disliked wet-lab research in biosecurity will enjoy wet-lab research in alternative proteins, but it seems less unlikely that someone who disliked wet-lab research in biosecurity will enjoy dry-lab research in biosecurity.
Similarly, if you enjoyed literature review based research in one cause areas, I think you are likely to enjoy the same type of research across a range of different cause areas (provided you consider the cause areas to be highly impactful).
I think decisions on cause areas should be made primarily on your views on what is most impactful (whilst avoiding single player thinking and considering any comparative advantages your background may give you), but decisions on roles / job types / work types should heavily consider what you have enjoyed and have done well.
I think rather than testing fit for particular cause areas, students should test fit for different roles / job types / work types, such as entrepreneurship / operations, policy / advocacy and a range of different types of research.
I agree to an extent, especially at the very high level that you're talking about -- if someone hates programing or wet lab research I think it is unlikely to matter what the program or lab is. However, within more social science type research / work I'm familiar with I don't view testing your fit with different types of research as mutually exclusive with testing your fit for researching within a cause area. In fact I think they're often linked since the cause area influences the type of research and work generally you'll be doing. To take an area I know well, law: it seems reasonable to me that someone who is interested in testing their fit in legal research or working as a lawyer generally would also benefit from trying working on different cause areas since the legal issues and types of research will be significantly different. Someone who enjoys trying to draft an international agreement to ban certain types of AI models may not be interested in doing domestic litigation focused on animal welfare. Though at a high level they could be called "legal research" or just lawyering, the day to day is going to be quite different.