With tubeless tires that lose pressure, the cause is often found in a leaking valve.
And such a double thing is often also the cause of the deflation. A leak valve is often too unmasked by tapping a finger with saliva on the valve. If the valve blows bubbles, it's the fault.
But the possible valve leakage can also occur during the transit of the rim. Because corrosion may have occurred between the rubber sleeve that holds the valve in place. And because air is thin stuff, things can go wrong there.
It is more often the case, however, that the corrosion-friendly light metal of the rim at the connection point to the rim of the tire is oxidized. A porous layer between metal and rubber is then formed.
The solution is to lighten the tire, to clean the shoulders of the rims and to reassemble the tire with a lick of tire grease.