Summary: what you know about protecting yourself from sunburn applies to your cat as well. Use common sense to protect your cat from skin cancer.
The difference with cats is that there are only two places, really, where sunburn is a genuine problem and that is the tips of the ears because the hair is very thin over the ear flaps. And white cats are particularly susceptible because there is no pigmentation in the hair strands because of the presence of the dominant white gene. That, by the way, is why some white cats are deaf and have blue eyes or odd-eye color. It's the same gene doing its work. The gene prevents the development of melanin in the iris of the eye causing it to be blue through the refraction of light.
So, you have an ear flap with very little protection in white cats from UVB and UVA. The ultraviolet light in the sun's rays penetrate into the epidermis and dermis of the skin damaging the individual cells of the skin. It damages the DNA of the cells which causes them to produce cancerous cells.
If you want to know a bit more about the science of how cancer develops from sunburn, you can click on this link.
Common sense dictates that the way you protect a cat from this serious health condition is to keep them inside during the hot weather. This may be difficult but I'm told that in America around 7/10 of the cats are indoor cats anyway. That said - and this is not common sense! - most UVB is stopped by the glass in windows and therefore an indoor cat snoozing under the sun behind the glass of window should be okay in terms of getting sunburned ears. But check this point if you wish.
We know that cats like to find little pools of sunlight and the home if they are confined to it. I'm waffling a bit but you simply protect the cat from the sun if you want to protect them from sunburn. Common sense. Sunscreen, as mentioned, is an alternative. You can buy sunscreen for pets online on Amazon but you might wish to consult with your veterinarian before purchasing it.
And if you cannot confine your cat during the hot weather because they insist on going out it'd be wise to provide shady spots in your backyard. Cats will normally find the shady spots but the problem here is that some don't because if they did, they wouldn't get sunburn on their ear flaps, would they?
It is interesting that you can buy an ear wrap for dogs. It's a band which goes over the ears. I am thinking aloud. If a cat could wear something which protected the tips of their ear flaps that would be a winning result. The problem is that cats wouldn't realise the benefits and would simply do their best to get it off. And they'd succeed. They may also have a tendency to wash off sunscreen. I'd watch that.
The bottom line on this topic is that you have to keep your cat indoors if the weather is really harshly hot with bright sunlight throughout the day if you want to guarantee protecting your cat's ears from sunburn. This will certainly apply much more for all-white cats than other coat types.
P.S. At the other end of the spectrum frostbite can also lead to the amputation of ear flaps (and paws). Once again, a cat's ear flaps are particularly vulnerable because there is very little covering of fur.