Should work OK for the rear but not the 21″ front. The 21″ front isn’t a safety rim so if it becomes low on air there is nothing to keep the tire from coming loose off the outer rim porches without a tube inside (very dangerous).
Rear is a safety rim so good to go as a tubeless once you seal the spoke area.
Still a good upgrade for the rear as the rear is a pain to remove and repair on the road or trail. Front is much easier to remove the wheel, and without a safety rim the front tire is easily removable from the rim.