I’ve been on a number of cruises and haven’t had any issues. I make sure to bring snacks for potential overnight lows, and our room stewards have been pretty good refilling the ice bucket morning & night to keep my insulin cold when I didn’t have a refrigerator in the stateroom. Usually lots of low carb options on the buffet menu, and you can tell your dinner wait staff to hold the carbs - on Royal Caribbean, we were paired with another couple for dinner, and she had celiac disease (severe gluten intolerance), so the head waiter made sure we could look at the next night’s dinner menu to prepare accordingly. They are usually very accommodating for people with food restrictions, just be sure to ask.
The only issue you may run into is taking snacks/food ashore in foreign countries. I’ve personally never had an issue (and have never been searched for food), but I usually bring a tube of glucose tablets along.
Security getting on the ship is looking for weapons & smuggled alcohol, not insulin or medical equipment. And the x-ray machine doesn’t detect my pump or CGM sensor, so no “additional screening” like at the airport.
In light of the recent quarantines on ships, I’d also recommend bringing enough insulin & supplies in case there is a delay getting off the ship.
Hope this helps! Have fun on your cruise & hope to see you on board someday!