I have to give the disclaimer that I do not have Stealth PPF and I could be totally wrong, but if I did have Stealth I would either use a spray coating specifically developed for matte paint and PPF (such as Gyeon Q²M Cure Matte described in my post above). Or I would choose a ceramic spray sealant that contains no carnauba wax or other waxes. This is from an older blog post on Dr. Beasley's website, but I would imagine it still applies:
"Why You Can’t Wax Matte Paint Finishes
Wax and matte paint are mortal enemies for one reason: wax gradually begins to reverse the ‘flat’ effect. Waxes are most commonly known as protection products that yield a shine, mostly because they’re made of carnauba and
filling ingredients. In basic speak, traditional waxes fill imperfections to create an even surface. Problem is, matte paint is full of imperfections. In fact, it’s those very imperfections and microscopic dimples that diffuse light rays and make the surface
appear non-reflective to the human eye."
Personally, I would email Xpel and ask them what they recommend for sealing and protecting Stealth PPF. My guess is that they are going to recommend their own PPF sealant or ceramic boost spray. And I don't think they carry or offer sealants specifically for matte finishes. You could also ask them if you choose to use a PPF-safe spray sealant that contains carnauba wax, would that have any impact on the matte appearance of Stealth.