How to make site private?

It’s years since I used WP – certainly pre- block editor and these support forums are very different. So I hope I’m posting in the right place.

I thought it was possible to make my whole site private but can’t find a setting in the dashboard. Tried to find an answer and think I have to use a plugin. Is that right? I thought I’d been able to make sites private in the past but maybe I’ve forgotten.

I know how to make individual pages and posts private but want the whole site private for now so someone who may run it with me can log in to have a look at it. And so it isn’t visible publicly by mistake. (Something weird is happening that it’s got a front page I didn’t create and that doesn’t show up in Pages or Posts in the dashboard and I can’t get rid of it. Maybe it’s from the theme I downloaded? Dunno. But it’s confusing won’t give my potential colleague a good impression!)

If I need a plugin, how do I find recommendations? There used to be a plugin forum here but I can’t find it now. Do I just have to search the plugin directory from dashboard and go through looking at reviews?

Sorry for dummy questions.

Thanks for your help.