Forget snacks entirely unless they are protein or vegetable. They grease the slippery slope to regaining what you have lost. I speak from experience. I am approaching RNY revision and I will not make the same mistakes again.
The pre-op food plan and the (clear/full liquid/puree) stages post op while we are not getting hungry give us the opportunity to establish a new way of eating. If we seek sugar-free or keto snacks we are merely making some substitutes for the OLD way of eating. It's too easy to find ourselves eating sugared and carbohydrate snacks and food when we don't happen to have the "-free" type.
Just because substitute snack foods are sold on bariatric sites does not mean they are good for us. If we are wise we will ignore those products.
Eat whole foods, fresh or frozen vegetables and fruits, quality poultry and meat products. Avoid sugar, sugar substitutes, wheat/flour products, and processed foods. We can get plenty of tasty food to eat with these choices.
I encourage you to obtain and read these two books by Dr. Matthew Weiner: A Pound of Cure and The Bariatric Guide and Cookbook. There are lots of other bariatric cookbooks available, too, including some for Air Fryers, InstaPots, and CrockPots. These will help you learn your new way of eating.