Like you my cars live outside. On my 997 (owned for 8 years) I used a Stormshield+ cover from Specialised Covers for many years. I cannot say I ever noticed any damage to the paintwork etc. This was a custom fit cover so unlike generic covers from Halfords etc fit the car like a glove making any movement of the cover very limited. Obviously only fitting the cover on a clean and dry car is essential. Ensuring you only cover the car when clean does mean cleaning it at the end of the weekend so you can cover it for the week ahead. In the end I got fed up washing it every Sunday afternoon and generally only covered it when I would not use it for a couple of weeks or more.
Having bought a 992 recently, however, my detailer who fit PPF and ceramic strongly urged me not to use a cover at all on my 992 and thus far I have not. That is despite having purchased the Porsche branded cover. On the latter, I am not sure I will ever be brave enough to use the Porsche cover as unlike the Stormshield which had a felt like interior lining, the Porsche cover is basically a fitted plastic sheet. To date, I have left my 992 to the elements and simply accept that it doesn’t always look it’s best.
All in all, based on my experience of a quality custom fit cover, I see no issue using one provided the car is properly cleaned before fitting. I think most advise against covers as there is clearly a risk of damage. But, if you do use a cover be prepared to clean the car and dry it properly before fitting.