How does the sun feel like in the Canary islands and similar places with mild temperatures?

Canary islands are fascinating to me because the temperatures are pretty mild, but the UV index is far higher than you'd expect by looking at the temperature only.

I'm from the Balkans and these days it's about 24, 25 celsius, with an UV index of 6 at noon, which is kinda medium-high, meanwhile in Las Palmas de Gran Canaria the daily highs are only around 21 celsius (colder due to the Atlantic ocean buffering), but with a mind boggling UV of 12, which is classified as extreme.

For reference, even in the southernmost parts of Greece or Italy in the peak of summer, it usually peaks at 10 or 11...so how does that feel?