You can test if a probiotic is actually alive. They may not provide the effect you want but they’re probably not placebos. The good ones at least.

Test I found if anyone else is wondering.

https://drformulas.com/blogs/news/probiotic-milk-test-how-do...

Can it be done with disposable syringes? They are available cheaply for kids's experiments and sometimes look more anaerobic than saran wraps.

You speak from a position of disparagement but I'm living proof ¯\_(ツ)_/¯

The world has no shortage of “I don’t understand this so it couldn’t be important” in daily life, let alone online.