I'm updating one of my macs to Ventura, but just to make sure: you have this little dot checked, right?
Upgraded my 16" M1 Max MPB to Ventura and Spine works as intended. If you do indeed have the dot checked, then we'll need more information from you. I.e. what input devices are you using, are you using any assistive software, screen tiling software, etc. Basically anything that could interfere with input to the Spine window.