Alternative for Celery salt and Coconut flour
The "celery" component of the salt is just there for flavor, and shouldn't affect how the dish cooks. Celery has a deeply vegetal flavor that can enhance others in the dish (hence why you see it in many soups, stews, and braises) but there's enough else in this preparation that you probably won't miss it much.

I wouldn't try to use regular flour, though. The coconut flour is being added here at the last minute to thicken the dish; regular flour will do this too, but unless it's cooked for several minutes it will retain a grainy, bready flavor. You might want to try a different common substitute like cornstarch, which thickens quickly and has a neutral flavor (it's also used in many American Chinese recipes). Whatever you do, be sure to follow the advice in the recipe and add it in very slow sprinklings, stirring in between so that it doesn't clump.