I have a folder that starts with a dot
. but am unable to display it in Finder.
How can I say that for folder x, Finder should also display hidden files/folders?
I don't think you can set this for individual folders. To set it globally, so that Finder always shows hidden files, run Terminal and enter the following two commands:
defaults write com.apple.finder AppleShowAllFiles true killall Finder
To switch back, do the same but substitute
This works all the way through macOS Catalina (and betas for Big Sur).
You can customize Finder through Terminal commands such that it defaults to show/hide hidden files.
To show hidden files and restart Finder:
defaults write com.apple.finder AppleShowAllFiles YES; killall Finder /System/Library/CoreServices/Finder.app
To hide hidden files and restart Finder:
defaults write com.apple.finder AppleShowAllFiles NO; killall Finder /System/Library/CoreServices/Finder.app