Settings is missing the possibility of making a site Private?

Regarding making a webshop private.

I had my old site at: https://hangmattor.se/
Then I made a new site at: https://utveckling.hangmattor.se/

When the new site was ready I moved the old site to:
https://old.hangmattor.se/
The new site was then moved to: https://hangmattor.se/
That worked fine.

I want to be able to access my old site at: https://old.hangmattor.se/
I want only Me to be able to see the old site.

To make the old site private, I’ve read that I should enter Settings – Reading
However, there is missing the option of Site visibility Public, Private etc.

The only setting available is allow/discourage search engines to index this site.

How can I make the site private when it’s missing in the settings?