Underscore not accepted in filename?

[Amber Martinell]

Why is underscore not accepted in filename for PhotoShop 21.2.1? Is it a bug or not?

[Nancy OShea]

Which operating system and version?

[Amber Martinell]

MAcOS High Sierra 10.13.6 (17G13035)
I was unable to save any file to my external drive, when I had the first
problem I got error mess saying FileName not allowed. But then I
couldn't erase files from the disk so now I believe It is not PhotoShop. My
drive had to be repaired.
Sorry to bother you.
1,5 TB is not done fast to copy.

Best Regards

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[JJMack]

Windows File System has no problem with  "_" in File Names.