ctype methods are used in a few places in Kirby, like the STR and A classes, in PHPMailer and the Laminas\Escaper class. So you would have to look closely where these are used internally.
Have you checked if PHP is really compiled without ctype? Check phpinfo() or on the command line with php -m.
Unfortunately I can’t check it because the client’s current plan does not include PHP at all.
So I thought before I tell him to upgrade to a plan which includes PHP, I should check if the requirements to run Kirby are even met. Guess I’ll just ask the company if it’s compiled without ctype.
Well, ctype appears when you do a php -m, but I wonder if they differenciate between standard modules that are usually included in PHP anyway and additional modules. I get a really long list of modules using that command. But you’d better check with the hosting provider. What sort of provider is that that doesn’t provide PHP by default? Sounds suspicious.