The City of St. John's Police Headquarters in the show is actually the Bruneau Centre for Research located on Memorial University of Newfoundland and Labrador's St. John's campus. Staff and students would see police related signage pop-up ahead of filming on their way to work/class, and the university would email notices to "not be alarmed by the appearance of police presence".
Based on the austrian show Kommissar Rex.
Thanks to Newfoundland and Labrador's public health measures and ability to keep COVID-19 cases low in 2020, production on season 3 was largely uninterrupted. Production was halted for two weeks after a crew member tested positive, but no ensuing outbreak was reported.
The series was filmed in the Canadian province of Newfoundland and Labrador, after which two breeds of dog were named. Rex, on the other hand, is a German Shepherd.
The St. John's Police Department is fictional, but there is a provincial police force in St. John's called the "RNC - Royal Newfoundland Constabulary. Outside of St. John's, the more commonly known "RCMP - Royal Canadian Mounted Police" have jurisdiction throughout most of the province. The RNC is in both St Johns and Corner Brook. The RCMP also retains a presence in both cities. Within each is a division where the RNC and RCMP are responsible. But the RCMP is federal whereas the RNC is provincial.