You can find the documentation here.
ImmichFrame can be opened with the link immichframe://open. If it is already running, the existing instance is brought to the front.
From Home Assistant, using the Android TV Remote integration:
action: remote.turn_on
target:
entity_id: remote.living_room_tv
data:
activity: immichframe://openFrom a computer with ADB:
adb shell am start -a android.intent.action.VIEW -d immichframe://open