The open/closed principle doesn’t say that. It says classes should be “open for extension” (usually meaning you are able to inherit from them and add functional

The open/closed principle doesn’t say that. It says classes should be “open for extension” (usually meaning you are able to inherit from them and add functionality) and “closed for modification”, meaning you aren’t able to change internal implementations. It does not say “everything should be closed by default unless explicitly marked otherwise”...