You can make sourdough starter using kefir (New England Cheese Making Supplies)
I make a sourdough Italian bread. Partial whole wheat with artisan white flour and powdered bone broth additive. I’m eating some right now dipped in olive oil.
I made a starter in 2018, using water and flour. Been using it ever since. There are probably close to a dozen others using my starter. One of my friend’s wives refuses to buy sourdough bread any more preferring to make her own.
There are numerous ways to make a sourdough starter. Wild or grapes off the vine, rye seeds and flour, and many others. Here is three ways:
https://www.youtube.com/watch?v=-n9yh5lDvts