No, the Amazon does not produce 20% of the Earths oxygen.  The real value is more like 5% to 6%.  This is NOT to minimize how bad it is to have out of control wildfires.  This is to keep unscientific non-facts from being perpetuated.  I was made to write this due to a statement seen on CNN. 

First let me explain from pure physics why it is impossible for an area like the amazon to be responsible for 20% of the Earths Oxygen production.   Oxygen is released for Carbon dioxide by photosynthesis in plants, all plants, from majestic trees to slimy algae living in the ocean.    In a very abbreviated way this is what happens.

1. You breath in oxygen and burn food with it and exhale carbon dioxide.
2. Plants take in carbondioxide, and with light (the photo in photosynthesis), release oxygen and bind carbon into sugars which we eat.
3. Repeat one and two.

Light from the Sun is what drives photosynthesis and most of the area of the planet is ocean.  70% ocean it means that approximately 70% of the photosynthesis, and hence of the oxygen will come from the ocean. 

Since the Amazon is not 2/3 of all the remaining surface of the Earth, or 20% of the total illuminated surface of the Earth it is mathematically, and physically, impossible for 20% of all the oxygen on Earth to come from the Amazon. 

There are a lot of details that can introduce variability into this. 

• Die offs of algae in parts of the ocean, blooms of too much in others. 
• Taking account of the percentage of desert and artic that are not vegetated
• Seasonal variations etc. 

That does not change the physical fact that only so much light can shine on the Amazon.  There is only so much surface area that can capture that light and play host to the green plants that release oxygen from carbon dioxide.  No matter how much biomass there is, only that mass which is catching sunlight can photosynthesize. 

Nothing in this article requires more than common high school biology and a bit of thought.   You, dear reader, could figure this out.  

The most reliable numbers from people who really study just this place the amazon as producing 5% to 6% of that total.   In fact the net production of oxygen by forest is nearly zero (No, the Amazon fires won’t deplete the Earth’s oxygen supply. Here’s why.)

The out of control burning Amazon is a tragedy and we should try to control and manage the fire cycle in a smart way.   It won't stop you from breathing.    The moral of this story, one moral, is think for yourself, think critically about claims.  The more unqualified and over the top the claims the more you should question them.