My cmake file seems correct. I checked with master branch and there were no warnings regarding fullscreen not beeing set. I reproduce the issue with the develop branch. What branch were you using ?
juce_add_plugin(${PROJECT_NAME}
PRODUCT_NAME ${PROJECT_NAME}
VERSION ${VERSION}
BUNDLE_ID ${VENDOR_IDENTIFIER}.${PROJECT_NAME}
COMPANY_NAME "XXX"
COMPANY_WEBSITE "XXX"
COMPANY_EMAIL "XXX"
COMPANY_COPYRIGHT ${COPYRIGHT}
IS_SYNTH FALSE
NEEDS_MIDI_INPUT TRUE
NEEDS_MIDI_OUTPUT FALSE
IS_MIDI_EFFECT FALSE
EDITOR_WANTS_KEYBOARD_FOCUS TRUE
PLUGIN_MANUFACTURER_CODE "XXX "
PLUGIN_CODE "XXXX"
AAX_CATEGORY AAX_ePlugInCategory_Reverb
COPY_PLUGIN_AFTER_BUILD TRUE
SUPPRESS_AU_PLIST_RESOURCE_USAGE TRUE
CUSTOM_XCASSETS_FOLDER ${CMAKE_CURRENT_SOURCE_DIR}/Images.xcassets
TARGETED_DEVICE_FAMILY "1,2" # iPhone and iPad
REQUIRES_FULL_SCREEN TRUE
IPAD_SCREEN_ORIENTATIONS UIInterfaceOrientationLandscapeRight UIInterfaceOrientationLandscapeLeft
IPHONE_SCREEN_ORIENTATIONS UIInterfaceOrientationLandscapeRight UIInterfaceOrientationLandscapeLeft
BACKGROUND_AUDIO_ENABLED TRUE
APP_GROUPS_ENABLED TRUE
ICLOUD_PERMISSIONS_ENABLED TRUE
MICROPHONE_PERMISSION_ENABLED TRUE
MICROPHONE_PERMISSION_TEXT "${PROJECT_NAME} requires microphone usage"
APP_GROUP_IDS group.${VENDOR_IDENTIFIER}.${PROJECT_NAME}
PLIST_TO_MERGE ${PLIST_TO_MERGE}}
FORMATS ${FORMATS})