All flow measurement tends to revolve around speed measurement. It's how car mass airflow meters work. there are plenty of differential air pressure sensors that have a logarithmic output to counteract the exponential increase in pressure differential across a restriction.
The challenge in the ventilator design is that it correctly interacts with the human body so that it works with the body, the result of working against the body is lung damage.
Although it is indeed challenging to make sure the ventilator correctly interacts with patients.
You also (ideally), want to make sure that the proposed hardware, performs safely (to specifications), despite changes to various parameters. When you start listing them, you can end up with a huge list.
Supply voltages, component tolerances, ambient temperature, mechanical variations, Oxygen percentage, air humidity, operator error, faulty Oxygen supply, etc etc.
Covering all those different things, can take years of research and development.
Otherwise, the machine could end up harming patients.
Presumably some sort of compromise to the usual required safety standards, has been taking place. I don't know how far they have gone, in that respect. Maybe in the future, there will be reports about it.
What engineers (electronic/mechanical) really need, is some kind of definitive specification, as to what is required and what will be accepted. Without such information, it can be very difficult to come up with proposals.
But it could be argued, that even a spec takes time to write and maintain.
I.e. The OP needed to realise this, and come up with such a specification, very quickly.
Maybe they did, maybe they didn't. I found it too confusing, with the OP, starting multiple threads, and changing the top of thread(s), on a daily basis. It got too confusing, at least for me.
I'm still NOT clear if it was an April 1st joke or not ?