Glare is fine to use on top of XPEL wrap. What you don't want to use is things like colored waxes, abrasives, and forgetting to removing stains immediately (bird droppings, etc). First off XPEL Ultimate itself is extremely stain resistant and has great UV protection and will not discolor, fade or get cloudy like other films on the market. Besides, yellowing on other ppf films is a result from lots of UV exposure. But wait - Glare Polish filters out harmful UV sunrays! As UV rays are the major cause of fading and the primary factor in the breakdown of polishes and waxes, Glare polish protects against all this so your car will not oxidize or fade. if anything, Glare Polish on top of Xpel Ultimate is actually going to make your car extremely shiny while also extending the life of the film even more than it's already guaranteed by it's own 10 year warranty! So it's a win/win.
fyi I have XPEL Ultimate and I am going to put Glare Polish on top of it soon.