It's hard to know without doing a placebo controlled trial. I eat Activia every day, but even I'm not sure it's having any effect and I don't trust Danone's own research. Overall, research seems to be mixed:

https://badgut.org/information-centre/a-z-digestive-topics/p...

Still, I think it's worth using probiotics, as there don't seem to be any negative effects.