Reaction training with no partner, is it possible?

YES.

Try training a turning punch / Tan & punch / Bong Sau etc. by using something out of your control as a trigger.

I find that if there’s a noisy dog next door, every bark throw a punch!

Don’t have a dog?  Put the TV on and the volume off, then, every time there’s a scene change, that’s your trigger (soap operas are the best for this but try not to lip read).

Enjoy