Since Firefox version 76 on macOS and Windows, you can be prompted to enter your operating system password (or authenticate using your fingerprint, face or voice login if enabled) when accessing your stored passwords in Lockwise on Firefox desktop.

To turn it on, enter about:config in the URL bar and set signon.management.page.os-auth.enabled = true.

Thank you @TyDraniu, I didn't know this option. I have set this option to true, removed my primary password and restarted FF (78 ESR). So I would have expected to be asked my Windows 10 password when accessing to the first password protected page but I'm not asked anything. What am I doing wrong?

but actually, if I want to look or copy a password in Lockwise, I am asked for the windows password...

Yes, it works like you said.

So, if I get it well, the password inside en you want to copy or see a password but in a password protected page, the user/password is filled automatically without any password protection?

Actually, this is not protecting really the passwords like the primary password does:

Using the "show/hide password" extension, on a password protected page, just by clicking in the "show" button near the password field, I can see the password (which is entered automatically without any protection as the windows password is not asked before filling)