I set up all the pages for my website (set as public & DRAFT) (https://9v7.961.myftpupload.com/?page_id=50) - BUT - lots of stuff not working (menu shows no pages, cannot link to Posts, custom changes not implemented, menu options (like set static or home page) not there. I am terrified to activate it (since it will replace my existing site). Will all these options magically appear once published so I can do a big clean up? I have tried multiple themes but now working with Wordpress Twenty Twenty one. Same problem with each one.
Possibly yes, possibly no.
I would recommend setting them to private and published so that you can see links working.
Drafts cannot be selected as menu links, nor do they have permalinks until they're published (only the shortlinks and only while logged in), so that is why they aren't working.
If you're afraid of taking down the site, create a backup, set up a "maintenance mode" to hide your site, and then do the switch and fix what you need to fix. Then remember to take the maintenance mode screen down when you're done.