It is better to think of a vacuum within air to be similar to a bubble underwater.
Air is like water in other ways too. We slightly "float" in air by the weight of air we displace. e.g. 80kg person is approximately 80 litres (density of a body is 1.010 kg/litre). Weight of displaced air is approx 0.1 gram (1.2929 gram/litre). So the floating effect of air reduces your weight (not mass) by about 0.1%.
> It is better to think of a vacuum within air to be similar to a bubble underwater.
I don’t think it is vey similar. That bubble pushes against the water to maintain itself; it manages to do that only because its “push” increases the higher its pressure and it is more compressible than water.
The vacuum, on the other hand, is compressible (if you want to call that so), but its “push” remains zero if you do, so it needs help to push against the air to maintain itself.
That’s why the post your replied to said “vacuums tend to collapse on themselves, I think it might be more costly in structural elements to prevent that?”
Air is like water in other ways too. We slightly "float" in air by the weight of air we displace. e.g. 80kg person is approximately 80 litres (density of a body is 1.010 kg/litre). Weight of displaced air is approx 0.1 gram (1.2929 gram/litre). So the floating effect of air reduces your weight (not mass) by about 0.1%.