I made some modifications to the Vectrex core to get XYZ output from the VGA port for an oscilloscope.
Here is my github fork with some more details and pictures:
https://github.com/Jokippo/Vectrex_MiSTer_XYZ
I included Gerbers and STLs so you can make your own adapter if you have some electronics knowledge.
Videos of it in action:
https://youtu.be/6vOpB0jy7xM
Lightpen:
https://youtube.com/shorts/xjpVvosmDCY