I see on my Win10 Pro localhost IIS PHP8:

• opendir("DataDir")
  attempts to open "DataDir" on the PHYSICAL Path, NOT under localhost, where PHP can work. If I set path "http://localhost/mySite/(php opendir here)/DataDir/" opendir() says that it is not a dir.

Sorry, it is not an answer on your question. In my opinion,it shows that PHP works incorrect in this function.
I can read (or write) any file with fopen("DataDir", "r"), but I cannot read list of files in this "DataDir". Copy code opendir() under "DataDir" does not work.

Vitaly Eremenko 2025-01-19