Future proofing your career especially in STEM fields is very important. New trendy fields and jobs pop up every few years and often the advice give is to run towards the new thing. This is usually one of the worst ideas as you get a shallow education as the field is new and you risk that field not being popular moving forward.
My advice is focus on the core skills or first principles. People think this means taking just a quick undergrad course or MOOC however this is far from what I mean. There are a lot of math, stats, and CS courses that focus on the fundamentals of areas you have never heard of. Really focusing in on the core skills will help you pick up new trendy topics much quicker. This whole idea is called "maturity."
Take a look at Thomas Garrity discussing mathematical maturity.
https://youtu.be/zHU1xH6Ogs4
Video version:
https://youtu.be/WTNM0yHF6vc
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