On YouTube to qualify as a partner and thus earn anything you need to (per their statement) "be in good standing with YouTube, have 4,000 valid public watch hours in the previous 12 months, and at least 1,000 subscribers." That's quite a hurdle before you can earn a penny.

Joanne Cooper who has been quite active on the forums here over the years uses her talent, determination and BiaB to get literally millions of plays on YouTube and has over 75,000 followers. And she has a great business model. No doubt her income is significant.

On the major streaming platforms, e.g., Spotify, you will, depending on various circumstances, earn $2-4 per 1,000 plays.

For both of the above you need to be very skilled at promotion. There are a zillion suggestions on how to do that. I am way, way too lazy.

Then there are the sync libraries where you can earn a few bucks or hit the big time depending on the placement. We have had some monetary success with Songtradr FWIW.

Bud