I tried draggin/dropping another installer into the Terminal, and it worked (it was the iPerf utility). I'm having a different issue trying to run iPerf, but that's another story... At least I know dragging and dropping files into the Terminal works.
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There are probably many people have stayed on the macOS for reasons like software wouldn't run on the newer version like Big Sur or even Catalina. But in your case, hardware is more difficult. With software, there's always a chance that a vendor may change code to support the newer version.
Some hardware vendors will figure out how to make it work but others will have to wait on collaboration with Apple to do so (e.g. 3rd docking stations that use display link software). I think I stayed on Yosemite a good while, finally just gave up on the docking station.
The big issue with staying with the current macOS is security bugs that will no longer be updated after the EOL. After a while, the next update will always be the next OS.
While you can probably remain functionally problem free, I would say that upgrading is something to consider especially because of security patches.
Thanks for the feedback Ronnie. Looks like it's not possible with my system. My Macbook Pro late 2013 model has Thunderbolt 2 ports. Also, now that Apple has users tied into and synchronized with an icloud account, I have come to the conclusion I'm just asking for major issues trying to do this, even if I had the latest hardware. I guess I will be forced to use the Turbotax online version next year.