A bug in iOS 14.5 Public Beta 1 will cause photos/images in GoodNotes not to load correctly but instead show a grey placeholder. Another symptom of this bug is that photos can’t be added or go missing after being added to a notebook.
To solve this, please update to iOS 14.5 Public Beta 4, or downgrade to the regular iOS 14.4.
In general, we recommend being careful when installing beta versions of apps or new operating systems as they may break the functionality you rely on.