Sheet has password-protected itself

I went to open and edit a calc file today. I cannot edit one sheet in the workbook because it’s protected and password protected. I DID NOT DO THIS and nobody else has access to my computer.
I need this sheet for a Department of Transportation request - we all know how patient government is…
Please help!

Are you sure it’s password protected and not just protected? Try to unlock with an empty password.

Tried that. Tried several different possible passwords, but didn’t work.

Shrug, don’t know. A sheet does not set itself as password protected.

If it’s .ods or .xlsx file format your last resort might be this FAQ.

Is there a backup of this file from before this became somehow protected? Thought of a backup on an external drive or if you are on Windows there is a chance with ‘previous version’ if you’ve enabled this function.

(I agree with @erAck that this does not happen by itself.)