They... they did what?
The question is not where, or who, or how, but rather when
Detroit stood as the first major U.S. city to instate Prohibition"\ -- "instate" should be "institute"
A tunnel of psychedelic lights connects Detroit Metropolitan Airport’s A and B/C Councourses to an original soundtrack. -- "Councourses" should be "Concourses"
Almost as quickly as the law was enacted, underground smuggling and speakeasies began to appear, with some experts estimating Detroit’s river crossing to Canada -- I think Word thinks wants a "that" before "Detroit's." I don't agree.
Below ground, an elaborate tunnel system connected the Fisher to New Center and General Motors buildings to ease employee commute. -- should be "commutes" or "commute times."
A tunnel system connects each of the hospitals making safe, seamless travel -- comma after "hospitals", add "for" after "making"
The steam loops ran on coal until converting into natural gas in the 1970s -- should be "converted"
The unique system of service tunnels set a precedent for surrounding shopping centers, although they were off-limits to the public and remained closed and unpassable after the mall's closure in 2015 -- I would have written "impassable" but "unpassable" is correct
What else?
Either that or like fictitious entries in dictionaries or trap streets in maps to catch plagiarists.
I suspect they rely on an automated spelling & grammar checker. Even that should have caught "councourse" but maybe because it was capitalized?
"instate" actually IS correct (my bad) but "institute" would be much better.
The other errors would get past a spell checker.