I’ve had ich before on my clowns but they were white spots, this is almost like biggish white marks on the fins. I notice he gets chased around a lot so not sure if it’s damage or not. There currently in QT
When it's only on the fins, many times it is only lymphocytosis...a virus that can be normal and resolved with less stress, good stable water parameters, and healthy foods.
If you start seeing the spots showing on the fish's skin and the same spot goes away in a few days and others pop up, then consider ich.
Chromis are very susceptible to Uronema, so watch closely for that on the fish.
Lymphocystis is pretty rare in green chromis (can show up though). I can't rule out ich, the photos just aren't clear enough, not uncommon for fish to have multiple issues at the same time. It does look like it is getting picked on. They are in QT - are you dosing copper? You may need to isolate this one to keep it from being attacked.