The same happened to me. Unsplash and Pixabay icons are not available in modern layout, only on visual and classic editor layout.
Solved it:
Change settings:
Hide Typography Section –>Yes
Save settings
Hide Elements Tab –>Yes
Save settings
Unhide Typography
Save settings
Unhide Elements Tab
Save settings
It worked fine again after doing this.
Forgot to mention that Settings > Design Tool > Image Options has Pixabay and Unsplash enabled. Nevertheless, Frontend doesnt show these options in Photos tab.
