Resolving the no external monitor signal error after updating Ubuntu 24.04

After installing system updates on my Ubuntu 24.04 Thinkpad P53 with a NVIDIA T1000 GPU, sometimes my external HDMI monitor will no longer get any display signal from my laptop after rebooting. This happened to me many times over the years; and every time I had to search for the solution to the problem. This could take a while and wasted my time. So for posterity's sake, I am writing this post so that I can refer to it in the future.

If the Ubuntu system updates borks up your external monitor display, you can do the following:

 Check if the NVIDIA drivers are installed correctly

1. Open up a terminal and type in the following command:
   
   $ sudo nvidia-smi
   
   
2.  If the above command shows a table as shown below, then your drivers are installed.
   
   
   
3. If not, then try to find and install the correct NVIDIA driver. 
   
   

Finding the correct NVIDIA driver for your system

1.  In a terminal, type in the following command:
   
   $ sudo ubuntu-drivers devices
   
   
2. In the following list that appears, take note of the recommended driver, e.g. nvidia-driver-595-open.
   
   
   
   

 Configure Ubuntu to use the recommended NVIDIA driver 

1.  Click the Ubuntu icon on the desktop and then choose the Additional drivers icon. 
   
   The Software & Updates dialog box appears.
   
   
   
2. In the list of drivers, toggle on the recommended driver, e.g. nvidia-driver-595-open. Then click Apply Changes. 
   
   
   
3. Reboot the machine.

 After restarting, the external monitor should be displaying the signal from the laptop.