That is incorrect.

N95 and P100 masks are available with and without valves.

One of the purposes of the exhaust valve in a respirator like this is so that moisture from exhalations does not build up in the mask, forming droplets, which then drip onto the finish surface that you are staining/sealing/painting.

This is a problem when performing fine finishing as a drop of water can wreak havoc in the finish you are applying.

Not all of them. For example, the two masks pictures here do not: https://en.wikipedia.org/wiki/N95_mask.

No, that is not true:

"Some disposable N95 masks come with an optional exhalation valve." https://www.honeywell.com/en-us/newsroom/news/2020/03/n95-ma...