The majority of extant keyboards at this point are probably laptop keyboards, followed by cheap rubber membrane boards. “Mechanical” keyboards are a small niche. I would guess desktop mechanical keyboards for commercial/office use are probably still bigger than the consumer market, but I’m not really sure.

I don’t have any data about the number of keyboards still in active use / still in working order, but the number of mechanical keyboards produced 2–3 decades ago was probably an order of magnitude larger than the number produced today. And while most have been scrapped by now, keyboards are pretty durable.

The past few years has seen significant growth in the number of people buying mechanical keyboards though, so you could be right that new devices make the majority.