You absolutely can (an example includes programmers who decide to work in computational biology and learn more biology from textbooks to better understand the job).

However, there is a substantial barrier for a programmer to switch careers and become a microbiologist: access to lab equipment. Part of the job of a microbiologist is to work with (usually expensive) scientific equipment to carry out and design procedures for experiments, and it’s hard to study independently without owning a lab space or the equipment. I’ve also found less educational material for self-study online.

Contrast this with self-study in programming. The required equipment is also just a low-end computer, and you don’t need a laboratory environment to develop your skillset. Educational resources (e.g. Automate the Boring Stuff With Python) are also not only widely accessible, but often free.