Ask your chemist, but I would be happy to eat probiotics provided it was a few hours before/after I took metformin. But why not try live full fat yogurt, check the yogurt has had nothing added to it, as you want it as low carb as possible.
The numbers of live bacteria in some probiotics are little more than negligible. I read in Moseley's gut heath book that the numbers are very small and that they then have to run the gamut of the hydrochloric acid in the stomach and finally they have to fight for a space to live in the gut. He says prebiotics are better but that in general a healthy diet is enough to keep the gut biome balanced. Moseley also states that artificial sweeteners have a detrimental effect on the gut biome and that once out of kilter it can take months for the balance of different bacteria to recover.