> I looked and looked on Amazon for protein powder that was not sweetened. Couldn't find any.

I'm surprised to hear that. Unsweetened, unflavoured, pure whey protein is a standard product for most supplement sellers. A search for "unflavored protein powder" on Amazon finds all sorts of things (many out of stock, some actually flavoured, but some suitable):

https://www.amazon.com/Unflavored-protein-powder/s?k=Unflavo...

I doubt you'll find flavoured but unsweetened protein powder, though. For some reason, savoury flavours of protein powder is not a thing.