Uniphy Platform Designer Error: "Cannot find sequencer/sequencer.elf"

Yes. In my opening paragraph of this forum post I said,

Prior to Quartus Prime Std v19, Intel used Cygwin for the Nios II Command Shell. Version 19.1 and beyond, they switched to using Ubunto 18.04 TLS and Windows Subsystem for Linux (WSL) to operate the Nios Command Shell. Here's a quote from the following support article.

https://www.intel.com/content/www/us/en/support/programmable/articles/000074066.html

"Starting with the Nios® II EDS in the Intel® Quartus® Prime Pro Edition software version 19.2 and Intel® Quartus® Prime Standard Edition software version 19.1, the Cygwin component in the Windows* version of Nios II EDS has been removed and replaced with WSL."

So, prior to Quartus v19, the Platform Designer used Cygwin instead of WSL to run the Nios Shell used to generate the projects.