Scope for PHP Variables Assigned in functions.php or a plugin

Nope! There is no way.
variable scope is file based in PHP, It means you can’t access a variable or even function and class from another file unless you include that file inside current file or use other similar ways like namespace or API call to get desired value from the file.

you can read more about variable scope in PHP:
https://www.php.net/manual/en/language.variables.scope.php