No problem, let me just say that I haven't tried it myself but I've watched a lot of videos of other people trying it and the worst results that I've seen have been the ones using a gel that they paint onto the plastic and then cover in plastic wrap. This tends to leave a streaky effect because the substance is not equally thick in every area and so it has more whitening effect where it's thicker.

The best results that I've seen have been the ones that have completely submerged the plastic in a liquid peroxide solution, or have suspended the plastic above the solution to immerse it in the vapors that evaporate off from the peroxide (pure oxygen). These methods give completely uniform coverage so they whiten the plastic equally in every place.

It seems that you also need strong UV, and people that live nearer the equator have better success using the sun. But in the absence of good UV lighting, heat also seems to have some effect.

Good luck!

Fair warning it will also continue yellowing and getting more and more brittle if you do nothing. Plastic doesn't biodegrade, but it does undergo aging in a way that makes it less durable than traditional materials. Wood can be kept from biodegrading, metal can be kept from corroding, but aging plastic just gets more and more brittle and just really wants to become microplastics

Look up a cleaning solution called 'RetroBright'. It's designed to remove the yellowing from the ABS housings of old electronics. I'm pretty sure the recipe for it is available free online, or you can order pre-mixed bottles of it. You have to be a little careful with it because it's mostly hydrogen peroxide, but I hear it works great.

You are correct, it's the plastic. Or rather, the fire retardant mixed into the plastic.