Is it safe to run an appimage in silverblue? Will it cause any harm to system?
That depends on the appimage - only download and run appimages that you trust. Best would be to verify the downloaded file with a GPG signature.
cause harm to system
Depends on the appimage. Only download and run appimages that you can trust. Never run an appimage as with sudo privileges.
You can read a heated discussion that shows a few pros and cons about appimage here: