Lookup tables (LUTs) define transformations to be applied to an image's colours in order to achieve a particular visual style. They are managed in the Adjustment panel.
Your Affinity app can import LUTs in several file formats:
If the imported add-on is a .cube, .csp, .3dl, or .look file, it is added to your chosen category in the Adjustments Studio.
If the imported add-on is an .afluts file, the new LUT category is automatically displayed in the Adjustments Studio. You may need to scroll to see it.