I would start with the valve - cheapest to fix and easy to diagnose with a dilute solution of washing up liquid smeared over the valve end.
Assuming you have tubeless tyres fitted without tubes it could be that the fitter damaged the sealant that is used on the spoke ends in the well of the wheel.
Or, it could be a standard slow puncture - wheel off and look for a leak in a large bucket of water (the plastic skips sold for gardening are good for a wheel rim to be rotated through).
You could always take it to a good tyre fitter.
