What’s the process when you’re ready to finish treatment for retainers, attachments removal, whitening etc.?

I’m a bit confused by the timeline!

I’m on my 3rd batch of refinements (this batch was just to fix my posterior open bite) and I think I’m good to go! The last 3 of my 14 trays are passive trays.

What’s the timeline once you confirm you’re ready to finish? Like, surely you need your attachments off to be scanned for your retainers, but if you get your attachments off then your passive aligners surely won’t stay in place properly while you’re waiting for your retainers? When does teeth whitening happen in that timeline? Will I leave my next appointment with my attachments removed and my teeth whitened and looking perfect, or is just for the retainer scan? I’m confused.

It’s been 15 months so far and I’m really excited and so so ready to finish NOW so I want to know how this goes so I can be prepared!

Thanks.