I would check very carefully the condition of the drains, rain rail, check under the deck carpet, door seals etc. I’d be surprised that a factory vinyl roof would be becoming porous.
Wearing my professional hat, mould requires warm, humid conditions; the roof lining, afer many years, becomes coated in an oily substance (skin, smoke stains etc), providing a good substrate for mould and fungi. Sitting in the car, with the heater running, provides a great environment. The tendancy for most people is to try and wipe it off, but you usually end up just reinnoculating other parts of the roof. I’d recommend making up a 0-5-1% v/v bleach solution, and carefully dabbing, let it sit for 20 minutes, clean off with fresh water, and monitor it. 1% dilution wouldn’t wreck the lining, stronger solutions might. The anti-mould sprays are better used as a preventer, once you have sorted out the original issue.
Although the door seals etc might not seem to be leaking, have a good look by lifting the carpet; the deck carpet is particularly problematic, as there is a damp-proof membrane; the carpet can feel dry to touch, but water is running under the membrane. The insulating materaial becomes sodden, and holds moisture. In extreme cases, the non-painted part of the shelf literally rusts away. If the roof drains are damaged, or detached, the area behind the seats becomes wet. Up front, the front seals can dribble down the a-piller. Also, under the footwell carpet, there is another damp proof membrane. On the drivers side, this becomes cracked. Wet shoes wet the carpet, water goes through the membrane, and again causes a insulating layer to become a sodden mess. There are also some taped over holes (used for the loom on lhd cars); if the tape has come off/is missing, moisture can get in, and it might not be immediately apparent.