The protein powder gives a lighter texture but you can substitute as stated in the note: "It’s best to use whey protein powder. However, the protein powder could be replaced with vanilla collagen or almond flour and vanilla extract."

Can you use something else besides whey protein

You can but you may need to add vanilla extract and sweetener to taste.

It's a stevia liquid sweetener that contains glycerine. If you can't find it, an equivalent sweetener is fine to use.

Did you freeze before baking? If so, the butter may have been too cold. If you get the temperature right, you should get cookies aren't too puffy or flat. Mine have never been dry so you have had too much flour.