Hi
@Aminanisa,
Don't worry.
1. it's a normal behaviour from OBS. You are recording your screen and OBS is showing your screen in the small screen. It's a loop.
2. your screen is bigger then the canva, so your need to get the screen capture size to fit your canva.
3. select the macOS screen capture source and do the shortcut CMD + S.
4. go in the macOS SCreen Capture properties and check "Hide OBS fron capture"
Cheers,