When it's less important, I just tell everyone what they see, but in order from worst perception check to best.

Then I give player with the best check a chance to give voice to how their character alerts the party.

If they choose not to, then I ask the players to honor that the other PCs don't know what's up.

At least one shambling horror creature has gotten a free pass this way when only the Warlock noticed it.

Warlock: "I say nothing."

GM: "It waits, then seems to give you a knowing look before wandering away into the woods."

Had a nice illusion room in a dungeon, where only one player was seeing the reality. I pre-prepared the notes, so no extra overhead in the session. That one player was also cursed with not being allowed to speak, but that info was also in the note, so the others didn't know. He tried to warn the others using sharades, and they thought he was cursed with mind control and turned on him, until he could convince them otherwise. That was a really fun round.

That's how they did it on that DC superheroes show with Sam Witwer. He'd pull the person aside and show them their real character sheet, and it was up to the player to decide what to let slip or not.

We called that a side bar. We would take the dm to a separate room to discuss an action

Honestly, SCP-4971 feels like a great bait and switch warlock hook to use on an experienced player. An oops your the bbeg moment. Either that or a prologue campaign to open in, and a second campaign where the good guys have to gather enough sacrifices in time.