Of these I only know about genetics/biology. You need an undergrad level textbook (I used Stryer's but you can usually get assigned textbooks from the course pages for the intro courses of your desired field at the tier 1 university of your choice) to skim through and a research assistant position in a related lab(volunteer is fine). The textbook will let you ask people already in the field questions without sounding like you're a lost Ancient Roman, and the assistant position will provide an environment in which people are constantly telling you tidbits about the field that will eventually let you read papers.

Once you can read and understand a paper and present it to your peers and they recognize you as a peer, you "know enough" about the field to contribute to it, and you don't actually need to pay for the degree to get there. But it might take decades anyway.

I think same applies to AI except in AI the lab can be an industry lab and the textbook can be 1st year calculus and linear algebra + a MOOC.