TLDR - Only install VivePort in the default installation location on the C drive (Windows 10 OS), do not change the installation location!!!
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I was just having this issue as well in January 2020, and I haven't seen any solutions posted anywhere about this issue. I resolved my issue though. I encountered the "you'll need a new app to open up this viveport" error a few times while trying to install VivePort, and each time I would completely uninstall Viveport and then try a new clean install and I kept getting this error. I had Viveport installed on another PC I have and it was working perfectly, and the only difference between my other PC install and my current PC was on my current PC I was trying to install VivePort to a secondary SSD and not my Windows C drive.
So after multiple failed attempts of try to install VivePort to a secondary SSD, I finally let VivePort install in its default install location on my C drive, and everything worked perfect, I stopped getting the "you'll need a new app to open up this viveport" error and everything just worked! I have been playing for days without any issues!
@VibrantNebula it seems there may be an issue of changing the default install location or installing on a separate drive that is not the Windows C drive.