This password specifically refers to "Password to Modify" and Excel 2019 / 365 clearly warn in the reenter password popup:
> Caution: Password to modify is not a security feature. ... Malicious users can edit the file and remove the password.
This type of "protection" is also present in the VBA blobs (where you can change a few bytes and work around the VBA protection)
Saving a file with a password to open actually employs encryption. The exact setting can be tuned with registry settings, but is typically AES-128-CBC.
Saving a file as "read-only" encrypts the file with the standard password "VelvetSweatshop"
> Caution: Password to modify is not a security feature. ... Malicious users can edit the file and remove the password.
This type of "protection" is also present in the VBA blobs (where you can change a few bytes and work around the VBA protection)
Saving a file with a password to open actually employs encryption. The exact setting can be tuned with registry settings, but is typically AES-128-CBC.
Saving a file as "read-only" encrypts the file with the standard password "VelvetSweatshop"