Will a clay-bar remove a ceramic coating?
Quick answer: Generally no -- a clay bar won't strip a properly cured ceramic coating, but it can mar the finish and diminish hydrophobics. Only clay when you need to deal with a specific problem, use plenty of lubricant, then apply a maintenance topper; full removal needs machine polishing.
The clay bar itself does no harm to the coating. What the clay picks up is another matter.
A clay bar is a sticky block that lifts metal particles, grit and other contaminants off the paintwork. Once embedded in the clay, those particles are dragged back across the surface as you work, which causes light scratches and swirl marks. When decontamination is needed before machine polishing, that abrasion is acceptable because the polish removes it. On a finished, coated car it just dulls the surface.
In practice, we rarely reach for a clay bar. A chemical fallout remover is the first tool out. Iron particles and industrial fallout dissolve on contact -- the product bleeds purple as it reacts, then rinses clean. No dragging, no abrasion. For bonded contamination that chemistry won't shift, we use rubber decontamination pads rather than clay. They work on the same principle -- physically lifting contamination off the surface -- but the rubber is softer and far less likely to trap particles and grind them back across the paint.
If you do need to use a clay bar, work with plenty of lubricant and keep the bar moving. A clay bar used dry, or with insufficient lubrication, will cause more damage than the contamination it is removing. Follow up with a maintenance topper to restore the hydrophobic properties the claying will have partially dulled.
We would advise against using a clay bar as part of your regular washing routine. A proper wash followed by a chemical decontamination step every few months is the better habit -- it keeps contamination down without the abrasion risk.