RPGMemes

Similarly, send each player a message that says "You are not the traitor."

Alternatively: Message that to the group as a whole, then say whoops you only meant to send it to one person directly. Never send it to anyone directly.

I accidentally (almost) did this for a one-shot.

I gave the players a brief scenario summary and three of them choose secret-aligned-with-the-enemy or mercenaries working for the enemy. The last, unwitting player, chose to be a goody two shoes good guy.

Before it really got off the ground, the players were expected to step in and stop some bad guys from beating up a commoner. The 'good guy' did, and all the bad guys and bad players turned on him.

It was a little funny but a big sigh moment when they figured it out.

Friend Computer says you want to look at Paranoia

If people here know Jet Lag: The Game on Youtube, the creators of that actually did this for real on their Nebula series The Getaway

On a drive across the American West, six creators must weed out the “snitch” sabotaging their $10,000 prize. The twist? They’re all the snitch.

https://nebula.tv/videos/getaway-trailer

Ah, so you're playing Paranoia then

Paranoia ttrpg

So basically Wendover's The Getaway. That was fun...