It may be because of the existence of tires and tiny trachoma that the tire leaks slowly. You can pump the normal tire pressure first, and then put the whole tire together with the hub in a large water tank to see if there are any bubbles. If there are bubbles, it means there are trachoma in this part.
It may be that the tire valve core is aging, and the aging of the rubber sealing ring of the valve core leads to slow tire air leakage.
It may be that the aging of the hub leads to the slow air leakage at the joint between the tire and the hub.
The above three points are common slow tire leakage, and the specific fault points are recommended to be determined after inspection.