Do you mean adding a custom texture to the ground would make it work? If so will it show regular Fortnite assets in there? For Sudoku I used regular floors found in Fortnite assets that change as the numbers change so updating regularly is helpful, so the mini map shows the updated Sudoku board.
Edit: I tried a few different texture assets for the ground from Sketchfab andPolyHaven and in a different map and it didn’t make it work.