So I was searching for this fix myself and found many old links that didn't work, including someone claiming the Origin version of Sim City 4 Deluxe could not work widescreen with custom resolution.
While the Origin client does offer a built in way to add additional command line arguments it just doesn't seem to work.
Instead you need to find where the Sim City 4 executable.
For me it was at:
Though for most it will be the C: drive.
Once you find the exe file right-click on it and create a shortcut.
Then right-click on the shortcut and add the code in red to the target box.

Once done you can then move the shortcut to your Desktop or anywhere you want it.
The various parameters are explained here.
The only thing you may want to edit is the custom resolution values:
The above is 1920 pixels wide by 1080 pixels tall and 32 bit color. (You could also use 16 bit color which probably won't even be a noticeable difference.)
Even if you have a 4K screen (3840 x 2160) you probably don't want to use that resolution as the controls will be too tiny too see. Even at 1920x1080 you'll need a good eye to see and zooming in and out may be a challenge on a touchpad, just too fast. Remember the number keys 1,2,3,4 and 5 will instantly bring you to one of the five zoom levels and + and - keys will zoom you in and out as well.
With this info Sim City 4 Deluxe was perfectly playable even on a modern high red, widescreen, Windows 10 system via the Origin client.