Shortages happen when demand exceeds production capacity, or if prices are artificially capped to make increased production unprofitable.

Usually the more of a product is bought, the more get produced. If the world will need more ventilators over the coming months, the best thing is for everyone to buy as many as they can right away.

There aren't that many "ultra-wealthy" people who are going to hoard ventilators. Even if they did buy them as an impulse, it would be an unusual scenario for them to sit unused in storage while the local hospital has patients going without them. Even the ultra-wealthy will value their friendly relations with the local ICU doctors more than that box gathering dust in the corner and donations will happen.

I personally know a couple of very wealthy individuals who bought ventilators.

So they bought ventilators. Did hospitals run out of ventilators? No. Did they even get to use the ventilators they bought? No. What's the problem then?

Actually, yes, there was a lack of ventilators in hospitals in my home country at some point. Luckily, not for long, as it's one of the countries which produces them. I can imagine that some of the neighbouring countries had it worse.