Well...

You can take a regular CRT and rewind the deflection coils on the yoke to work as a vector CRT display. Arcade Jason has a good video on how to do this.

https://www.youtube.com/watch?v=Ci9qiGVMF7s

Then you need a vector generator if you don't have an OG vector game. This one on Github is pretty good and can be connected to either an oscilloscope or vector monitor.

https://github.com/english1234/vstcm

If you use the vstcm to drive your rewound crt, you still have a problem. The deflection coils are very low impedance (around an ohm I think), so you need an amplifier stable at very low impedances that can generate a voltage sufficient to get deflection across the full screen in x and y. I think Arcade Jason was working on one of these too but I don't think it is out yet. ElectronAsh was working on one as well but I don't think he finished it.

https://www.youtube.com/watch?v=tybGveLtlkA

https://github.com/ElectronAsh/Vector-XY-Deflection-Board

Or you could follow iz8dwf's amazing series on how he built a black and white vector monitor.

https://www.youtube.com/playlist?list=PLbKEoUHtoVucsrySlogDz...

Turns out that’s what a Vectrex is! Or can be. As a pointless weekend project, I opened up my Vectrex, disconnected its logic board from its analog board, and gave it a new controller so an external computer can drive it. It doesn’t look as good, because the clever circuitry in the original to keep the beam velocity consistent lives on the digital board, but I think I can fix that in the controller firmware. Yet another post for my nonexistent blog.