Novo and LV are the only games in town I think when it comes to wrapped cars (PPF is a wrap, albeit transparent, but the principals are identical).
Admiral I believe cover you with a wrap, but the wrap isn't covered which is to say if you have an accident you have to get the affected panels re-wrapped yourself at your own cost.
I'm not aware of any other companies covering them, I did quite a bit of hunting around earlier in the year before I renewed with Novo.
Plenty of people I imagine just don't declare it, because to do so would cost them more money by having to go with someone else, or don't think that PPF is a wrap so either don't mention it.
Frankly repairing a wrapped car must be a bit of a nightmare. For starters paint shops and companies that handle wraps often aren't the same. They are two completely different disciplines that require knowledge and expertise. In the event of an accident, therefore, you'd have to get the car repainted and then presumably it would need to be then transported to a wrapper to reapply the wrap. This complicates the repair and adds additional cost. Secondly, I'm not even sure you're supposed to wrap a freshly painted car. I would presume you aren't - which means it has to cure for a period of time before it can be safely wrapped, which equals more time (and more loan car expense), etc.
I went with Novo for the first two years of insurance on my M3P mainly because they were Tesla-centric and I liked aspects of the policy (agreed value on the car, fully comp drive other vehicles, Tesla loan car in the event of a claim, etc). They were expensive in the first year (~£900 if I recall) and even more the second year, because of a new underwriter. I'm dreading my renewal in March.
I am very much of the mind though that I want peace of mind when I have insurance for something. I don't want to just find the absolute bargain bucket price that either doesn't properly cover the car, or I have to omit information like the PPF and risk not being covered at all. A piece of paper that just says I'm insured isn't much value to me.