Broad ask for recommendations for online, heavily quantitative masters programs

I am not entirely sure about this. With your background, devoting the time spent on a masters program to digging into something on your own instead (and maybe contributing to relevant projects, or papers as a coauthor) could be a better investment. YMMV.

MSc/MA level programs in econ usually do not exist separately because they are just the first 2 years of a PhD, and the stuff they teach is relevant for the latter. That said, most US econ PhD programs give you an MA degree after two years, and occasionally people stop there.