Can a ceramic coating protect a car from bird droppings?
Quick answer: A ceramic coating will resist and slow the etching, but bird droppings should be removed as soon as possible.
Depending on what the bird has been eating, droppings can be highly corrosive -- they contain uric acid at a very low pH, which reacts quickly with the clear coat on unprotected paint. Ceramic and graphene coatings are very good at resisting that chemical attack -- the uric acid reacts with the coating rather than the paint, and the reaction is slowed significantly. But the droppings still need cleaning and neutralising as quickly as possible, because they will cause damage if left.
Heat speeds the reaction up. Bird mess on a hot bonnet or roof can cause damage in hours rather than days. If dried bird poop is stuck to the paintwork, do not use hot water to soften it.
Keep a soft cloth and a purpose-made bird-mess remover in the boot so you can deal with mess as soon as you spot it. Baby wipes or wet wipes are worth carrying too. Wipe the bird mess off, spray the area generously with a bird-mess remover to neutralise any corrosive residue, then buff off with a soft cloth. At the earliest opportunity, wash the area with soapy water using a pH-neutral shampoo -- baking soda added to the soapy water neutralises the remaining acid.
If a bird leaves a mark on a coated car, it is almost always because the droppings were left for too long, the panel was hot for an extended period, or there was contamination already sitting on the coating that should have been removed during decontamination first. The coating's job is to slow the attack; yours is to spot it and get it off.
For the broader "why have ceramic paint protection" answer, see What are the benefits of a ceramic coating?.