I have flown many times with a RyanAir (and many other airlines) since being diagnosed with diabetes.
In my experience, the airline has no interest in whether you have diabetes.
Airport security may be interested ... although rarely.
Personally, I do not mention my diabetes to anyone (it is not their business) unless they ask a specific question such as "do you have any sharp items in your luggage?"
(I enjoy answering this one with a "Yes" and a long gap as they start to panic before adding "I have diabetes".)
There is a great page on this website with instructions for travelling:
https://www.diabetes.co.uk/travel/air-travel-and-insulin.html
Regarding taking a repeat prescription, I have a letter from my diabetes consultant which lives with my passport and comes with me on every flight.
In 15 years and well over a hundred flights, I have only needed to show this once but, without it, I would not have been able to fly. So I consider it a type of insurance.
This is more than a repeat prescription as it states that I must have the medication in my hand luggage and mentions the possibility of "death" if I do not.
I know others just take their repeat prescription and have no issues ... or even need to show it. So the choice is yours.
You mention having a "diabetes bag". Is this in addition to your single piece of hand luggage that RyanAir allow?
I know some travel with a "medical bag" but I am a "once bag only" kinda gal so have no experience with convincing the "hand luggage police" to allow me to take extra. If you can get your diabetes stuff in your main bag, this may be easier.
Unless you have a pump, you should not experience delays or issues.
(And airports are getting more familiar with pumps so the delays are becoming less prevalent).
If you are going on holiday, have a great time.
If you are going on a business trip, I hope the meeting goes well.
If you are visiting family, I hope they are all well.