I still haven't come across this island, the glowing moss island or the bells island either. Weirdly enough I came across a YouTube video from a ACNH player who has this theory that the mystery islands you get via Kapp'n is down to how long you've been playing ACNH. So if you've not been playing a full year or recently restarted your island your less likely to get the rarer islands such as the shooting star island or even access to all four seasonal islands until you've played through the season on your own island. So if you reset in summer you'll only have access to the summer island for now but once you play through Fall, Winter and Spring then you'll have a higher chance of getting those islands in the future when you go on a Kapp'n Mystery Island Tour.
I don't know if there's any truth to this theory but it does make more sense for those who are getting the same islands over and over at the moment, myself included.