For type 1’s over time, it’s typical for the condition to affect the duodenum, and that slows digestion. But this depends on type of diabetes, the length of time you’ve had it, and if the duodenum has been affected.
Now if you just looking to slow digestion, fatty cheeses will do that. Like mozzarella cheese. Apply a healthy coating of that to food and it’ll slow the whole works down by a couple of hours.