Wikipedia has an article on "modern portfolio theory", and there are textbooks. Portfolio Visualizer
https://www.portfoliovisualizer.com/ has tools to find historically optimal porfolios. R has many packages for empirical finance:
https://cran.rproject.org/web/views/Finance.html . You can peruse the Chartered Financial Analyst curriculum:
https://www.cfainstitute.org/en/programs/cfa/curriculum . Wilmott is a site for derivatives quants:
https://wilmott.com/ . There is an algo trading sub-reddit:
https://www.reddit.com/r/algotrading/ .