Title. I've tried troubleshooting for hours, disabling antivirus, messing with .vdf files, god knows what else. The message says:

"Content on this drive not managed by Steam. This could include your operating system, documents, other applications, ect."

It's a brand new 1TB SSD drive with nothing on it, aside from whatever system files were downloaded in order for my pc to be able to use the SSD.

What could be the issue? Thanks.