Greetings joerumst,
We see that only certain photos are able to be seen in the Photo app on your iMac and we understand the importance in being able to see the preview of these. You've come to the right place for assistance with this.
First, we'd recommend checking to make sure that the iOS version is fully updated on your iPhone 11 as you're not seeing this occur with your iPhone SE. Just in case you'd like to take a look at the steps for updating your iPhone, check them out here:
Update your iPhone, iPad, or iPod touch
If you see that an update isn't needed for your iPhone, let's set up a test user account to see if the same image previews aren't being shown there. This will help to isolate whether this is related to your user account or the communication between your Mac and iPhone. For assistance with setting up a test user account, check out the following resource:
Set up users, guests, and groups on Mac
We look forward to hearing back from you.
Cheers!