What was the technical work you did? Was most of your time spent on market research, coding, blockchain, or designing/implementing algorithms?

I would pick one or more job titles that are both relevant to the job you're applying for and to the work you did and put those on your resume, e.g.

Crypto trader/blockchain developer/investment analyst (self-employed)

- Developed trading platform with X latency

- Implemented blah blah algorithm

- (Throw in more metrics about how you were able to beat competition)

The proof is the skills you built along the way, the same as any job you put on your resume. In data science, at least, we're rarely asked for references. Don't think of yourself as unemployed during that time, and especially don't call yourself unemployed.