When you switch to the HDMI mode on your TV and it displays a no signal status, it means that the other display source wasn't connected properly. If you're connecting via a Windows 10/11 PC, ensure that its duplicate or extended display settings have been turned on. Also, it should detect and connect to the TV display easily.
If you're connecting via PlayStation or Xbox, do the same, check on those devices. Finally, ensure that your HDMI cable has been inserted properly in the right television HDMI port.