Not tubeless wheels??

Either these wheels require tubeless rim tape in order to be set up tubeless, or the valves you are using (which are really too short for the wheel depth, by the way, which will make some pumps hard/impossible to use) do not properly seal the valve hole in the rim, meaning air is escaping out that hole and into the rim cavity.

Valves come with differently shaped rubber bungs, and picking a shape that matches your rim best is important. If the bung is not well matched to the inside of the rim channel, air will escape out the valve hole, even with sealant and a tight nut on the outside. Some rims require conical bungs, some require a rectangular bung, some will only work if the valve itself has rubber that extends into the valve hole itself, like on this DT valve: https://images.performancebike.com/images/large/bikes/dtswiss/tvxxxxxs09710s.jpg

If the end of the valve is too wide, and hits the tire itself before it can be properly tightened against the inside of the valve hole, it can be impossible to get a good enough seal. I’ve had this issue with Orange Seal valves on narrow rims. The circular end of the valve is pretty wide, meaning it hits the tire before sealing the valve hole. https://cdn.shoplightspeed.com/shops/607788/files/43147203/650x750x2/image.jpg

That little hole is to prevent pressure building up in the rim cavity. You want that little hole. Without that hole, you likely would have already destroyed that rim by pumping the inner cavity full of pressure until the thin sidewall, which is not meant to be pressurized, cracked or exploded.

Have you added sealant?

I posted the same question a week ago or so. I think it was the valve in my case. However, adding some sealant pretty much stopped it immediately and I haven’t lost any pressure for at least a week.