Locking multiple notes

Sorry, but does not seem possible.

Lock notes on your iPhone, iPad, iPod touch, and Mac:

https://support.apple.com/en-gb/HT205794

But once the locks are set for multiple entries, entering the password for one note will open all the locks for protected content.

Closing the application shuts all the locks, so all the notes with locks on are protected upon restarting the application.

You are also restricted in the content that can be password protected:

Removing locks also has to be done note by note:

More for Locking & Removing locks.

Once any protected note has been opened, you can apply a lock to other entries:

Control-Click selected note:

or Menu bar > Notes > File > Lock Note:

& Remove any lock to a note

Control-Click selected note:

& Menu bar > Notes > File > Remove Lock:

Nb. none of the above can be used for more than one selected note.