Fluent Bit itself doesn't include an automatic startup mechanism as it's primarily a log forwarder and processor. However, you can set up Fluent Bit to start automatically at boot by creating a system service for it.
Enable the Service
Enable the Fluent Bit to start at boot by the fllowing command,
sudosystemctlenablefluent-bit
Now, Fluent Bit will start automatically on system boot.