video preview

Create a test meeting through your Zoom portal.  Scroll down to VIDEO section and look at what is set there.  I'm guessing yours is set to OFF and grayed out.  That means its pre-configured in your settings.  You can look at where this setting is being enforced, whether its at the user level, group level, or account level.  Happy hunting.

Are you on an licensed plan or basic?  After you go into your Zoom portal, click on SETTINGS, then make sure MEETINGS is selected at the top.  Scroll down to the "Schedule Meeting" section and you should see HOST VIDEO and PARTICIPANT VIDEO settings.  These control joining a meeting with video on vs. off.

 Just found this:  Note: If you don't see the Screen option, it may be due to the Disable desktop screen sharing for meetings you host setting in the Zoom web portal.

Located in this documentation:  https://support.zoom.com/hc/en/article?id=zm_kb&sysparm_article=KB0066104

There’s nothing like that for me under meetings. Nothing to scroll either.

Definitely something on the phone then.....try looking at iPhone SETTINGS, Zoom and see if anything in there needs to be adjusted.  Otherwise not sure, good luck.

Did you ever find a solution to the missing video preview?  Mine used to happen automatically, now I can't find any way to turn it on.

I'm wondering if Zoom stopped it in the basic plan, so if you want to see how cadaverous you look before a meeting you have to have a paid membership.  Grrrr.

This happens, as Zoom support just explained to me, because the scheduler can schedule the meeting with video off.  Zoom then assumes you don't want to see your video before you turn it on because it doesn't turn on automatically.
Personally, I think if you check the "Always show video preview" checkbox as a user, you should ALWAYS see your video preview before your camera starts transmitting video!  It shouldn't have anything to do with what the person scheduling the meeting thinks or whether your video starts automatically.
The logic is that a video preview is only shown when the Scheduler sets video ON and you have the video preview setting checked and you don't have "Turn off video when joining" enabled.    Terrible UX design!