I think it is pretty conclusive that sunscreen wearing will improve your skin complexion and smoothness in the long term (presumably the effect is not worth having if you never go outside in sunshine, obv).
Whether it has enough material effect to do anything to your risk of dying from malignant melonoma (which is pretty rare anyway), is more of an open question. It might not be a worthwhile trade-off for everyone.
It is true that cloud cover doesn’t reduce UV as much as one might think, certainly. But there is a *huge* difference in UV levels between Winter and Summer in Northern Europe. Appopriate levels of sun-cream cannot plausibly be the same regardless of time of year. Time of day also makes a huge difference; if you’re not going outside within 2-3 hours either side of the zenith (in theory noon; in practice moves up to 2 hours off this depending on exactly where you live, local time zones, and daylight saving), you can mostly forget about sun-cream.