Welcome, Ola.
The Necchi Supernova is a high shank machine, it had a special attachment for making buttonholes. Most of the White buttonholers I have seen have been for bottom clamp machines. The Singer buttonholer would be for a low shank or slant shank machine. From my understanding, buttonhole attachments have been around for around 160 years, consequently there have been many variations and improvements. Bottom line is more than likely the attachments you have will not work on the Necchi Supernova.
The Necchi Supernova is a very good machine with tight tolerances. If you can find a reputable sewing machine service person with vintage machines, I would recommend getting it serviced. It can be done by yourself, if you are so inclined, but would recommend a lot of research and a desire before doing so. I have heard of repair person actually ruining a machine or trying to trade it in for a new plastic machine, that is made for planned obsolescence and lots of $$$$$.
We like pictures. In order to post pictures on Quilting Board, you will probably need to reduce or compress the picture to a
file size that is smaller than 2MB. How to post images can be found at
https://www.quiltingboard.com/attach...020-01-17-.pdf
Don't forget to scroll over to the far right to find and click on the "
Upload" button.
Janey - Neat people never make the exciting discoveries I do.