Don't make (all) encounters like this
The encounters seem static and staged because, as described, they are static and staged. It feels like the NPCs are in stasis until the PCs turn because, well, they are.
So, don't do that.
Instead, prep a timeline of events that will happen if the PCs don't interfere. All that's needed is a basic understanding of the relevant NPCs' motivations, intentions, and capabilities.
For your example, the guys on the outside have some motivation to want the driver dead (this may need more elaboration ... or not), they intend to kill him, and their capabilities include a chainsaw. The guy on the inside has some motivation for not dying (probably a given for everyone), an intention to avoid the guys with the chainsaw, and the capability of whatever is inside the car.
What we see here is a moment on the timeline so let's back it up and consider the whole thing, appreciating that I have no idea how this fits into your adventure and no knowledge of the Cyberpunk Red system but it should give you the idea:
- 22:00 victim leaves the party
- 22:08 victim is chased by assailants
- 22:10 victim crashes off-road
- 22:12 assailants try to get into the car
- 22:15 assailant 1 gets the chainsaw
- 22:18 they cut their way in
- 22:19 they cut the guy's head off
- 22:24 they leave the scene
Now, you can write this in times, days, rounds, or whatever fits your needs/system.
Now, the PCs can intervene at any point in the timeline.
- They could take the victim from the party by a different route in which case the attack never occurs. Referring back to the motivations, the assailants will probably come up with a different plan.
- They could delay the victim. How long will the assailants wait?
- They could go with the victim. Then they can intervene in the car chase.
- They could follow the victim. They could intervene in the chase, in the attack, or just watch it all play out.
- They could miss the whole thing and learn about the gruesome chainsaw murder in tomorrow's paper.
Now, however this plays out, it won't feel like the NPCs were waiting in the wings of the player's story - it feels like there is a whole dynamic world out there.