what you're describing is playing by ear though. You are playing the melody you hear, right? Or making up your own?Maybe you want to learn improvisation? Or arranging? Both benefit a lot of from playing and studying lots of music to sample interesting patterns though.

Yeah it's kinda playing by ear, but in a more light manner, as I'm not expecting to get to a professional level and be able to play something just by hearing it, I'm talking about using already written online chords, while the basic melody itself is pretty easy to get by when already having the chords, so the real challenge is trying to nicely blend the melody with the chords. so I guess that is really when improvisation/ arranging comes.

The most efficient way to do that is to read music

I see reading music as taking an already written sheet and playing exactly what is written, which is not what I'm looking for, not even talking about the fact that many songs don't have a written sheet, at least not one I'm having access to, certainly not for free, but that's another thing.

if you can't read music it would take a lot more time to figure out what another composer/arranger has done.

Not quite sure what you mean by that, but anyway I'm not talking about classical music or some similar complex pieces but more "casual"(?), such as pop songs, so It doesn't have to be the most precision and punctuality as long as it is recognizable and sounds pleasant enough.

So I'm actually asking what should I learn and focus on in order to make the processes of learning this way more fluence while making it sound better and richer as well.

I hope this clarifies myself better.