Hey Carlos!
I was in a similar spot once upon a time, so I wrote an article about how I'd get started as a Ruby on Rails developer in 2023. Here's a link if you're interested:
austn.net/the-3-best-ways-to-learn-ruby-on-rails-…
I'm biased, so I recommend Ruby, but I've seen a lot of openings for JavaScript and PHP lately as well.
As far as part-time sites, I've used Upwork before and have had a good experience with it. WeWorkRemotely, Indeed, and LinkedIn can all be useful as well
Best of luck to you, let me know if there's anything I can do to help!