cinematic mode icon not there on my iMovie on iMac

You need to click on the cinematic clip in the timeline in order to make the cinematic button appear in the toolbar above the viewer.

The cinematic editing controls will appear when you click on the button. If iMovie is not providing you with the above editing tools try deleting preferences and see if that cures the problem.

Take a look at the thread in this link and see if anything in there helps you:

Cinematic editor not shown in iMovie - Apple Community

-- Rich

Are you clicking on the clip in the time line? You need to do that before the cinematic editing will appear.

If you’ve tried the other suggtions in this thread and accompanying links, with no success, try calling Apple Support and talking to the techs there. They have the capability of remotely accessing your computer that we cannot do here. Click on the Support item at the top of this forum’s screen and navigate ta place where you can enter your phone number.

— Rich

Im my case, I don't even have this icon to click on. I check the clips, and they are all marked as cinematic in library.