When it comes to deleting, it is always best practice to err on the side of caution!
When outside of Setup, it doesn't matter which window is shown on the internal touchscreen when you tap DELETE. After tapping delete, you then choose what you want to get rid of.
To get rid of a group/palette/macro, tap DELETE, and then tap the item on the touchscreen. To delete a playback or UDK, tap DELETE, and tap the playback or UDK's button. To delete a cue, tap DELETE, type the cue number, and then tap the button of the playback you wish to remove the cue from.
When in Setup > Fixture Schedule, the DELETE behaviour is reversed - you first select the fixtures you wish to remove, then tap DELETE, then confirm. Any fixtures with LEDs lit below their channel faders, will be deleted if you confirm the delete operation.
https://www.zero88.com/manuals/zeros/patching/fixture-schedule/deleting-fixtures
The next software update (ZerOS 7.14) should help improve this (the next beta version will include these enhancements, reference number ZOS-8853).
Hope this helps,