The way it works is that the attacked country invokes article 5. If the country does it then other members are obligated to help. If they don't, they are undermining NATO.

Having said that, NATO doesn't specify how countries supposed to respond. It could be something to this: https://en.wikipedia.org/wiki/Phoney_War

I think putin sending Wagner to Belarus is indeed thinking to force Belarus to attack Poland or a Baltic states and see what happens. Of course that would be simple, it would be Belarus vs NATO, and would end up quickly.

So he is tipping the scale and saying that attacking Belarus will be also attacking Russia, hoping that it will be ignored like two Russian missiles hitting Poland. If it won't be ignored, then he is just sacrificing Belarus.