Hey there! Due to player shenanigans, the party's stealth bunny has found their way into the enemy big bad's secret base. The session wrapped up around that point. I want to take the player into a 1 on 1 session before my group meets up again, where only he will be able to see the rolls he makes, the character chat in the text log, etc. as to keep it a surprise for when the rest of the players get there, or in case of the sneaky not making it out alive. Is there a way to do this without making an entirely different game and not having any of my maps/tokens/character sheets set up there?
Sort of. You need to split the party: https://wiki.roll20.net/Page_Toolbar#Split_the_Par
... And then make sure that the player always whispers the GM and has their character set to whisper the GM.
Alternatively, copy the campaign, and only invite them.
Yeah, copying the campaign would be the best way.
Why not simply have the 1 vs 1 and then clear the chat history? If worried there is important information there, can always save it before deleting it. Copying the campaign is always an option, but then you have to backtrack anything the character acquired back to the original game, or any notes you made as well. Usually not too bad I suppose, but when possibly saving and then clearing the chat log removes all the concerns. Use which is easiest or best suited for you.
Alright and, since I'm an idiot, how would you copy a campaign?
Wiki page: Copy game is the official information you are seeking. Basically you click on the setting button (outside the game table) and choose copy game which will take you to a page where you can rename the copy and choose what is going to be copied.