You can lock your public page behind a code. Visitors who do not have the code see a prompt instead of your page.
Setting one
Settings, Privacy, Access code. Pick something memorable but not obvious. We do not store it in plain text, only a hash.
Sharing the code
However you want: DM, email, group chat. Once a visitor enters the right code they get in and stay in for the session.
Removing it
Clear the field in Settings and your page is public again.