Since you have two different security domains here, the best way to go about ensuring isolation between the networks is to use a switch that can support vlans. With the vlans you can impose switch enforced isolation to keep the traffic from mixing. Just be aware that adding vlans to your network will impose a certain amount of management overhead. But this is the standard way to go about this.
Shop for 1-2 switch at Best Buy. Find low everyday prices and buy online for delivery or in-store pick-up. Nic number 1, goes to office network, and Nic number 2 goes to public network. That would minimize the amount work for you provided there is a data jack for each network near that single computer. If not, you could add a USB wireless adapter to the workstation, which would be easy too. Use your 1/4-inch open-end wrench, turning counterclockwise to loosen the lock nut. The lock nut secures the adjusting screw in place. The adjusting screw allows you to adjust the distance between the switch activator and the clutch pedal.
On the public wifi you will need to ensure you have the necessary services available like DNS and DHCP. These services can be supplied by your internet firewall or by adding additional devices.
One Switch 1.11 MacOS [Full]
One Switch
I want to introduce you to a new program that will help you quickly and easily customize your desktop. OneSwitch is a tiny application designed to increase your efficiency with fast access to several important switches. It can be opened in the menu bar, and it allows you to switch certain functions of the system with just a couple of clicks.
Features:
Hide Desktop Icons
Hide your messy desktop with one click.
Dark Mode
Toggle Dark Mode at any time.
Keep Awake
Prevent your Mac from sleeping or displaying the screen saver.
Screen Saver
Sometimes you will like to turn it on manually.
AirPods
Connect AirPods with your Mac in just a second.
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Requirements: OS X 10.14 or later 64-bit