You can do some of this at home too. I buy raw milk (it's common here in Switzerland) and make paneer or ricotta. Then I boil down the whey and make a fudge-like Norwegian cheese.
Another pathway is to start with 35% fat cream or crème fraiche and make butter. Then you use the buttermilk to make cheese. Then you use the whey to make Norwegian cheese OR if you started with crème fraiche you take the sour whey and make sorbet by mixing it with some fruit juice and shaking the container every hour or so as it freezes in the freezer.
It's not nearly as time-consuming as it sounds and the rewards are better than anything you'd buy. The butter is better (less water within), the paneer and ricotta are so much better than factory-made, and the sorbet is... well probably about equal to sour cream sorbet you'd buy (assuming you buy movenpick :).
where do you get the bacteria/ yeast from?
Easiest place to get it is from the product you want to produce.
For example, if you want to make yogurt then grab a little bit of the leftover yogurt in your fridge, drop a dollop of it in, and viola, it'll start the yogurtification process.
You can also rely on the open-air bacteria for some culturing, but the results can be all over the place. This is how a lot of sites suggest starting sour dough.
You don't actually need raw milk to make yogurt. I use Fairlife brand which is ultra-filtered milk, and combine it with a container of plain Fage (active culture Greek yogurt) in a pressure cooker. This is a very common way to make yogurt at home here in the US.
I also grew up on a cattle farm and have made many other products when I was younger from raw milk. There are /some/ things that require raw milk because they are wild cultured, but most food products are not wild cultured when made at home so you can pitch the correct yeast or bacteria with pasteurized milk just fine. One thing that is hard to find in the US and impossible to make without raw milk is Serbian/Turkish kajmak/kaymak.
I even make my own butter at home using ultra processed heavy whipping cream. Raw milk is a great thing in some ways, but it is not in others and in any case not really a requirement to make milk products at home.