How secure an OS is depends entirely on the configuration. A Linux install can be less secure than Windows or macOS, if configured so.

Linux tends to be more secure OOTB because distro devs tend to be security conscious. Android is also fairly secure, since it has no root access, sandboxes applications to a degree, and has other hardening employed. However, Android is also very vast and built for various devices by many manufacturers, so it also depends on them.