✅ Q about the "?" symbol when declaring vars

Hello everybody ,I have seen some c# vidoes where people declare variables with "?", for example "int?","bool?" , I have asked copilot what does it mean and he said that its just "normal variables" but they are special in that they can also store Null .

my question is : how accurate is his answer and in what case/context will I use :"type?" instead of "type"

thanks