We are running SharePoint Subscription Edition with the newest CU.
It is not possible to add an image to a modern page
1 Add image:
2 No prompt or anything to choose a picture
3 When I click on the edit icon, I get a white empty side panel
4 With the developer tools i get the following errors:
I can add the Pnp Modern Script Editor to add pictures to pages, but this can't be a solution for normal users.
Edit: I forget to remove some main url parts from the screenshots, that's why I was editing the question.