All food post gastric bypass should be introduced with caution. I would hope that the clinical staff have warned you about dumping syndrome which can affect blood pressure and glucose level meaning you’ll feel faint. You’ll need to ‘develop’ a new digestive response to food.
Huel is useful due to its low GI (caveat: the GI of a food may differ in gastric bypass). Start slowly, one scoop in water and sip this slowly. After 2-3 days, then one scoop twice a day, again slowly.
If you have access toa blood glucose monitor, then I’d check your BMs 3 x per day for the first few weeks until you get used to your ‘new’ system.
(My friend lost over 11 stone in just over a year with a similar op and feels great!)