Massive MIMO produces a 2-7X capacity improvement, far more than the 15-50% of 5G NR software. Every engineer knows the 5G hype has become ridiculous, especially because Massive MIMO is a key component of 4G.
Guido Weissbrich of Vodafone Germany confirms they have moved from trials to deployment. His colleagues are in production in Australia. Bharti in India is covering much of Kolkata, formerly known as Calcutta. Verizon is widely deployed in the U.S. but has released few details.
All of these, I believe, are below 2.1 GHz and are FDD. One vendor off the record guessed FDD Massive would only be a 1.5X improvement. Karri Kuoppamaki of T-Mobile expects a 2-3X improvement.