I absolutely HATE protein-powder that contains sweetener or flavor of any kind. There are a few companies that sell unsweetened and unflavored products. One company I like is Naked Nutrition -- www.nakednutrition.com. They have a product called Mass-Gainer. Some of their flavored products are called "Less-naked" meaning they have added a little sweetener and flavoring--these taste much better than other products. My son had a lot of difficulty gaining weight--still does. It is essential for a player to EAT a lot and EAT proper foods. This can be supplemented with protein shakes and it helps if they taste good!
My 2022 has been using Naked Mass for almost two weeks. Decided to try it after reading another parent's success and a little research myself. I can see extra weight on him already. He is eating a TON but I've now started to try to make it as easy and accessible as possible for him, even though it's a lot of work for me, I think we are making more progress because I've stepped in a little. Making sure there are EASY options in the fridge seem to be helping a lot. So even though he should do it, I'm prepping veggies/fruit that can go in a smoothie and leaving ready to go in fridge, stocking meat drawer with grab and go protein (cubed cheese, chicken skewers, steak cubes), trailmix made with weight gain nuts (and M&Ms because he's a teen boy) already bagged up in largish single serving portions, I just made protein balls that are small enough they can come out of the mouth of a shaker bottle so he can have them in his backpack and pop them in his mouth under his mask between classes. The biggest hit was disposable soup spoons right next to the peanut butter jar, and the Horizon milk boxes that don't have to be refrigerated in the mud room. He grabs those as he heads out the door, regardless if he's eaten or not.