I have a very important PSB file that won't open in Photoshop and says " could not open because of program error" is there anyone that could possibly help me solve this problem.

I'm looking for someone with advanced Adobe Photoshop experience who may be able to help recover or diagnose a very important PSB file.

The file is stored on an external hard drive and opened without any issues yesterday. Today, however, it refuses to open and Photoshop displays the following error:

"Could not open '[filename].psb' because of a program error."

There have been no Photoshop updates or macOS updates since the file was last opened successfully. As far as I'm aware, nothing changed between yesterday and today.

The file is extremely important, and I'm hoping to determine whether the issue is with the PSB file itself, Photoshop, or the external drive. Ideally, I'd like to recover the document with all layers and edits intact.

If you have experience diagnosing or recovering Photoshop PSB files, or have successfully resolved this specific "program error" before, I would be very grateful for your assistance.