In the end I think the normal rules apply, it’s not a liquid and it’s not exotic food.
Obviously given its dusty consistency it can cause some initial perplexity …
Taking Huel on a flight or in the hold is fine from a security standpoint. What you would need to check is if there are any specific restrictions on food in the destination country.
I think it’ll be fine. If it’s in the original pouch they’ll be able to see what it is, and you can get Huel in the US so it’s not some weird foreign powder.
Do not try to hide it by putting it up your arse. If anything that will make them more suspicious.
It will be fine as long as it’s in it’s original sealed unopened packaging.
Make sure you declare it though.
Undeclared food can land you with a £10,000 fine, and a lot of unnecessary hassle.