insulin is a growth hormone. it does cause weight gain. look up Dr. Bernstein's Diabetes Solution. he's an endocrinologist who wrote a book about all the ins and outs. also, he himself is a type 1 diabetic.
I simply cut down on carbs (no bread, rise, cakes...). Started loosing extra weight after a month...
Living with type 1 diabetes since 2017.
Insulin does cause weight gain. The more you take- the more weight you can gain. Since insulin is taken on the basis of your carbs, I suggest you stick to 80% protein,10% carbs and 10% fat in your diet. Eat a ton of fruits and vegetables and nuts