I can’t import Tiff images into Figma desktop on Mac, As I understand it should be possible.
Are you trying to just drag and drop in to a design file?
I get the same import error with this method, but if you create a frame and add a .tiff image as the fill image then I have no issues importing.
Doesn´t seem to do anything
There is no mention of TIFF support.
It’s not a supported format. Convert your file to something else.