A shop diagnosis is probably your best bet at this point. YOu can fix it yourself after they tell you what’s wrong if you like.
But back to the basics, if I had a car that would crank ok but wouldn’t start when cold but would start with some extra gas or starter fluid sprayed into the intake manifold, first thing I’d suspect is the cold start function is running too lean for some reason. The engine computer is supposed to inject much more gasoline on cold starts than hot starts. So either that isn’t happening, or there’s un-metered air getting into the engine. Either will cause a too-lean condition. For the former, start by researching how the cold start system works on your car. For the latter, ann intake manifold vacuum measurement and a proper vacuum system diagnosis is where I’d start. Best of luck.