Visible crew/equipment: When Winn is putting on his shirt after being caught, you can see his mic wire through the hole where Kara says he forgot to button his shirt. (00:03:15)
Continuity mistake: When Cat is on the talk show, the microphone on her collar keeps disappearing and reappearing between shots.
Answer: For one, it's usually cheaper to film in Vancouver because of the tax breaks. But all the CW Arrowverse shows (with the exception of "Black Lighting") are/were filmed in Vancouver. So it makes it easier and cheaper for sharing set designs, crossovers, etc ("Black Lightning" filmed in Vancouver during its crossover). Originally "Supergirl" wasn't part of the Arrowverse when it was on CBS, but it was too expensive to produce and wasn't reaching the wider audience the CW shows had. So CBS moved it to its sister company, The CW.
Bishop73