The Cloud Secret in Roblox Classic is a hidden collectible that awards you with the "In the Clouds" badge. Here's how to get it:
Spawn into Roblox Classic.
Head to the race car area, where you'll find the Character Doors.
Locate the red flower near the edge of the platform.
Jump down directly below the flower. You won't take fall damage, and you'll land on a hidden platform below.
Walk forward to collect the Cloud Secret and earn the "In the Clouds" badge!
There are many video guides available online that you can look up for more visual reference if needed