I think the term you would want to search on is "venous leakage" or "venous leakage erectile dysfunction." Here is the first link that popped up on google https://www.american-hospital.org/en/treatment/venous-leak-embolization
Vacuum erection devices often come with an assortment of such rings, which can also be bought separately. The goal is to take an engorged penis, place the ring as close to the base as possible to sustain the engorgement, and then remove it before it causes damage to the penis, but after enjoying the presence of such engorgement.
There are a couple downsides... 1) the penis extends into the body below the skin and the ring cannot be placed below the skin, and 2) since the blood flow is cut off, it quickly becomes cooler and the penis also becomes bluer as the oxygen is depleted. Of course, the third downside is if you leave it too long.... Well, don't do that.
Sizing and amount of stretch are important and personal, but some rings also have tabs or auxiliary rings to help with application and removal.