Mine's also painted black and was fitted in June 2020 (previous owner), it was bad when I bought it, faded in most areas and almost a matt finish. I tried polytrol and that was ok for a couple of months. In the end it came off with the jet wash, but even before that it had started fading again and it was never a good finish. I've resigned to the fact that it needs to be wet sanded and re-polished. I've tried a few times, but the weather has been so hot I really need a whole day of no sun or rain as have to do it out side. I have already 500 sanded the whole roof and then done parts with 800/1000/2000/3000. It's come up good, not yet perfect. I've cut an polished a small section and then waxed it and that looks good. Again I think it could be better if a pro did it, but definitely acceptable. At the moment I'm thinking cut/polish/wax and then maybe a ceramic coat to try and protect it, but may also just try to keep a wax coat on it every few months (without ceramic) and see if that works as it's easy to apply.
I wouldn't recommend polytrol, although it could definitely been the way I applied it. I think if I didn't try that I could have got away with just a cut and polish