Does anyone know how well Polypropylene withstands UV from lamps and the sun?

I know Polycarbonate tends to yellow and Acrylic/Perspex is quite stable but I haven't seen much lighting equipment made of Polypropylene.
From what I have read online PP does not stand up to being outdoors very well, but I have a 2D bulkhead with a PP diffuser that is intended for outdoor use, so maybe it has some UV stabilizers added?

PP normally becomes super brittle in my experience (using empty juice cups on homemade LED landscape lights). Are you sure the cover isn't HDPE or PET? I think both of those plastics are excellent at being UV proof

The PDF data sheet of the fitting shows it having a PP cover and an ABS base. I do recall seeing one of these fittings in the past with a cracked cover. It seems strange they'd use PP when there are other plastics that are better suited for the job.