Kitchen faucet low flow rate?
So it was the diverter that is in line with the faucet.
The valve inside the diverter is stuck down. It only moves a little up when the faucet is running. The valve in the downward position supplies water to sprayer which is why the sprayer was fine.
Interestingly if you cycle the sprayer on and off a few times the valve loosens some and can move upward more which lets some more water flow through the faucet for a period of time.
$14 for new diverter.