When setting the umask, does it only get applied to that directory or the entire filesystem?

Example as root user:
Does that umask get applied for the directory or the entire file system? Then it would be a bad idea to change it if it didn't affected the entire filesystem where distro packages update files and install new ones? The video I was watching created a group "research", added project members to it and created a shared directory located at the root of the filesystem. And then used umask on it and turned sticky bit on for it. But it sounds like a bad idea if it affected the entire filesystem. I've seen umask used in fstab, and it was for the entire filesystem.

see man bash:
The user file-creation mask is set to mode. If mode begins with a digit, it is interpreted as an octal number; otherwise it is interpreted as a symbolic mode mask similar to that accepted by chmod(1). If mode is omitted, the current value of the mask is printed. The -S option causes the mask to be printed in symbolic form; the default output is an octal number. If the -p option is supplied, and mode is omitted, the output is in a form that may be reused as input. The return status is 0 if the mode was successfully changed or if no mode argument was supplied, and false otherwise.
and see man mkdir

this is a file creation mask, it is used when you create new file/dir, it should be set before the mkdir command.

chmod is the command for changing an existing file/directory mode.
compare "chmod o-w /shareddir" with "chmod -R o-w /shareddir"


umask affects the mode of files/directories you create in the future. It's a value that exists in your process (e.g. your shell session) and not a value defined for a whole filesystem.
umask 022 ; mkdir u022
umask 027 ; mkdir u027
umask 077 ; mkdir u077
ls -lad u*
exit