12 volt water pump

Have to agree with others that the most LIKELY cause of your problem is the winterizing valve is set to draw from the antifreeze bottle instead of the FW tank. Reverse the position of that valve. It is usually located very close to the water pump itself. Also remember that it will take five or ten minutes to fill the water heater tank and you may not have pressure at the faucets until it is finished filling.

Be sure the valves are in their proper position including drain valves closed. Open all of the faucets and hope for the best. Is there an option for adding antifreeze to the pump (a flexible hose connected to the inlet piping? If so, close off the valve to the tank and open the valve to the hose and pour some water into the hose or dip it into some water at a level higher than the pump.
I've run out of ideas.
P.S. this is a common problem. Let us know how you solved it.

Check the connections at pump for cracks or even a 'winterizing valve' open (suction side of pump)

Did you run pump and open a faucet......hot/cold sides to get the air out of plumbing lines? Hot side will take longer..has to fill water heater tank first.

Do you gravity fill fresh tank OR fill via a valve on water panel?
If via valve on water panel......check that it is closed.
If open, pump will just suck water out of tank and then run it back to tank thru that fill valve.