Hi Geert,
Please go to Dynamics 365 Guides to check images in 3D forms under Content.
If images also not show in Dynamics 365 Guides, you can uninstall Guides solutions and reinstall.
Here is a reference link: Install the Dynamics 365 Guides solution - Dynamics 365 Mixed Reality | Microsoft Learn
Otherwise, uninstall and reinstall Guides to test if images will show.
Best Regards,
Sayen Zhang
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