Most parasitic infections won't show any outward signs. It's totally different from bacterial issues. Fish live with it for months so the fish should "look" just fine but perhaps not behave fine and will eventually show worse signs. Other common signs besides flashing are platies racing up and down the glass, shaking as if trying to get rid of something, white poop, getting thinner or getting bloated, stunted growth, deformities, difficulty breathing, etc..not all signs at once or even just one of them at a time.
If it's just one fish and the occasional flashing, I'd hold on for now, considering you've got shrimp. It still could be an irritant in the water causing it.
If it's a parasitic infection, a few months down the line you'll have more fish with it, one by one, not all at once. The symptoms may differ and not all species will be affected. Sometimes it's species related. Keep an eye on the platies in particular for a start.
Do large and regular water changes. Good water quality will prevent others succumb to types of parasites that only get active when the fish's immune system weakens. If it's worms, it won't help, it will eventually kill the fish but that develops in months, even a year or years is not uncommon. Don't get spooked either, most fish carry parasites or are surrounded by them but don't ever succumb to them. Preventative measures are the best, e.g. water quality.
As for removing the platy, you can if you want if you have another cycled tank. Don't put the fish in an uncycled tank to treat it as it will get worse. If you want to experiment, separate it and medicate it with a broad spectrum parasitic as kusuri. Providing the issue is not water quality related, if the meds "cure" that fish, it will certainly cure the rest. If not, then no point dumping meds in your other tank. But keep in mind that platies don't like being alone. It will stress it out additionally which is no good if the fish is sick.
Additionally, from my own experience platies carry hexamita, no matter where you get it from. It's a type of parasite common to livebearers, angelfish, etc.. but not bottom dwellers. They can live healthily with it for life but sometimes they can't fight it off. Waterlife octozin is active against it and is harmless to fish, plants, inverts and filter in the recommended dosage. Again, only the weak ones get sick and it's trigged by bad water quality. They carry it in the gut but fish die only when the parasites go into the blood stream. Then they'll die for sure. This is the advanced stage and it's very rare. Until then they've got chance to get over it.
I am only giving you some info. Think and observe before you act. Patience is the key when you are in doubt. Less action and more water changes are the best first approach.
You will not wipe out parasites or bacteria completely from a tank by medicating. It just decreases their numbers so the fish can fight it off via their immune system.
