"Features such as Ground Plane or Model Targets may work on devices not explicitly mentioned in the tables below assuming that the devices meet the minimum required specifications for the feature. For more information on the minimum required for Model Targets and Ground Plane, refer to the sections at the bottom of this page."
and down there:
"Ground Plane Minimum Requirements:
Android Version: 6.0 (Marshmallow) or newer
IMU w/ Gyroscope Sensors
Selective Image Stabilization"
which both mentioned devices fulfill, I suppose. Both devices work well with ARCore applications.
How is it possible that such powerful and flagship devices are not supporting spatial targets?