symlink whitelist works for files inside a world folder, but if the root world folder is a link or junction, the world cannot be loaded. the following error is printed in log:

Failed to read level World data
...\.minecraft\saves\World is not a directory

steps to reproduce:

create allowed_symlinks.txt in .minecraft folder with content "[regex].+"
create a world
move the world to .minecraft\test\world
open cmd in .minecraft folder
mklink /J saves\world test\world
restart minecraft and attempt to load into the world