Having a slow computer makes things tougher but where there's a will, there's a way. For example, last year I had to leave home for a few months and only had my phone with me. But, I was still able to code and publish console games from my phone during that time. When I returned home, I took the code that I typed up on my phone and I went into Unity and published my Sudoku android game with it. I am unfortunately all to familiar with the struggle of trying to become a programmer with no money to do so.
With a slow computer, big engines such as Unity or Unreal Engine may be too much although you might get away with Unity 2D. A safer bet might be creating MERN or FERN websites since those are pretty low impact. You could try RPG Maker but that's very restricting and not really programming. On that note, you could experiment with Python.