

There are plenty of legitimate reasons for Google to provide extra support and exceptions to parts of their guidelines to certain parties, including themselves. No one is claiming this is a consequence-neutral decision, and it’s right to not inherently trust these exceptions, but it is not a black and white issue.
In this case, placing extra barriers around sensitive permissions like MANAGE_EXTERNAL_STORAGE
for untrusted parties is perfectly reasonable, but the process they implemented should be competent and appealable to a real support person. What Google should be criticized for (and “heavily fined” by the EU if that were to happen) is their inconsistent and often incorrect baseline review process, as well as their lack of any real support. They are essentially part of a duopoly and should thus be forced to act responsibly.
This feels more like two questions, so I’ll answer them both:
If you’re trying to learn programming and know at least some basics, my only advice is to pick a project you’re even a little interested in and get started. Don’t worry about operating system, it doesn’t actually matter that much unless you’re working on iOS or MacOS! A weather app for whatever language/platform you’re working with is usually my first suggestion for students.