The Amazon doesn't actually produce 20% of the world's oxygen

The rainforest is often called 'the lungs of the Earth,' but its net contribution to atmospheric oxygen is close to zero: nearly all the oxygen its plants produce by day is reabsorbed by the same plants and by decomposing matter at night. The 20% figure likely confuses the Amazon's share of land photosynthesis with its share of the atmosphere's total oxygen supply.

— Wikipedia contributors, Amazon rainforest — Net atmospheric oxygen contribution