Alas, I can walk out on my veranda and see all the planes in the sky overhead,
but there is no corresponding function to do the same for a given rectangle of sky here on FlightAware.
Find an airport near you and enter the ICAO airport code in the “Airport Tracker/Info” box at lower left.
If you are in Taiwan, try RCTP for Taiwan Taoyuan International Airport. This will bring up a map and list of flights. You can then enlarge, zoom and scroll the map around to your hearts delight.
Try flightradar24 dot com. I am in the states and under an air route going east for KSJC, KOAK and KSFO and use both flightaware and flightradar24. And the ones I am not able to find, I “assume” they are military from or heading to Travis AFB.