With no project open, go to Settings > Libraries do you have an available location for storing assets set as the default. If not, you need to add one as Substance Painter store export presets in a subfolder in that location.
With no project open, go to Settings > Libraries do you have an available location for storing assets set as the default. If not, you need to add one as Substance Painter store export presets in a subfolder in that location.