If it's available for your device it should be on the "Camera Modes".
Open Camera > Photo > Settings > Camera Modes > Edit Modes > then
activate Instagram. But I don't think it's already available for Note 9.
If not, don't worry, you're not missing a...
Been using Nova launcher ever since! Don't know why Samsung can't even
make their interface as flexible! Hopefully, they include more interface
settings in the coming updates