Can you apply wax to a ceramic-coated car?
TL;DR Yes, you can, but you shouldn't — applying wax over a ceramic coating will not improve its performance; it will hinder it. You're essentially putting a layer over the coating, stopping it from working as intended.
I don't want to admit it, but let's face it, traditional wax is dead. Even today's lab-created synthetic concoctions can't compete with the power, protection, and durability of a ceramic coating. In addition, professional-grade coatings offer years of protection against UV exposure, bird droppings, tree sap, and other harmful contaminants.
Problems with wax
Some of the best paste waxes claim to last up to 6 months, whereas a consumer-level coating lasts about 2 to 3 years, and if you get a professional-grade application, this can last a lifetime when checked annually.
Car wax also contains a lot of natural oils, grease, and other sticky substances. This may produce the water-beading effect you see after a wax application. However, these also attract dirt, dust and other road contaminants, causing them to stick to the surface.
The key to the performance of your ceramic coating is keeping it clean and free of harmful contaminants that can accelerate the breakdown of these hard coatings, which is why a regular maintenance wash will support the performance of the coating.
Important — you should never use a clay bar on a ceramic-coated car; this will permanently damage the coating. Instead, it's more effective to use a selection of cleaning chemicals to remove these contaminations.
Conclusion
If you want to boost the gloss or improve slickness, apply a water-based product, like Gyeon WetCoat, when you rinse the car down or Gyeon QuickDetailer or Gyeon Cure as a drying aid.