I have always used a brush to apply milk paint and haven’t had the foaming problem, but where I buy the stuff there is usually a product next to the milk paint that is an anti foaming agent additive. It may be the brand of roller, but some other issue such as water hardness or ( more likely) softness.
Foam rollers for me have always been a crap-shoot. They work fine for some things and make a horrible mess with others. I have had good luck with lambs wool rollers with almost any type of finish so you might want to give those a try.
@1boardatatime Curtis’ video was interesting. It reminded me that the General Finishes milk paint probably isn’t really milk paint. It’s a thick acrylic made to look like milk paint. So, it may not behave as expected from its name. I’d like to try real milk paint now.