Note: This guide will be using the Barrier DEVICE, but you can use a prop if you want; both work, but I prefer the device.
Literally just put that barrier in front of your Vent Entrance. Like this:
Make the Barrier Active Scope Player, and make it not visible in game.
Now for deactivating the barrier. Just place a relay and a lifecycle. Make the Relay’s settings Relay Audience Specific Team, and Team is 2, or whatever team your imposter is on. Wire the lifecycle to the relay, then the relay to the barrier. The only thing you have click carefully is the relay to the barrier. Make it deactivate.
I hope this helps!
-@Blizzy