@Wookie is correct. For non-healthcare one provider CPR, compressions only. If you have more people, access to an ambu bag, are comfortable doing manual breaths etc., the recommendations change. They've found that people hesitated to provide CPR because of the need to give mouth to mouth. So if you just provide correct compressions, you can give CPR
You should
*never* ever ever give insulin to an unconscious person. Please, never do this. If a person is unconscious and a diabetic, you should administer a glucagon injection (sugar), not insulin. Adding more sugar to a person who has high blood sugar isn't great, but isn't going to kill them. Giving insulin to someone with low blood sugar *will* kill them. And most cases of rapid unconsciousness for a diabetic, it is low sugar. Type I diabetics *should* carry glucagon with them, hopefully, if they can afford it. If they are unconscious, do not try and get them to drink sugar or eat sugar, as they will likely aspirate. /end soap box as someone whose friend is T1
And no, we are not doing comparisons of different CPR types in the hospital. That's why the quality of evidence is typically low for out of hospital cardiac arrests.
Most important is: if someone's heart stops, start compressions and call for help. If you can give breaths and are comfortable doing so and it will not delay compressions, please do that too, but don't let it delay compressions for an adult. Focus is more on breathing for infants, but it still all about starting compressions and getting expert help there immediately.