UV protection, pff. It possibly matters in sailing and snow sports, where you’re often exposed to bright sunlight and reflections, but mountain biking has less UV exposure than walking to the shops and you don’t worry about that. It’s also much easier to make UV-opaque polycarbonate lenses than it is to make UV-clear ones, so the odds your polycarb glasses aren’t UV-protective are tiny.
You can easily test this with an LED torch and a roadsign, btw- most LED torches throw a lot of UV, which causes the road sign to flouresce. Shine torch through lens, look for change.