Wild ass guess, Antenna / cable problems. The Pi and associated hardware are working.
Pull up the FlightAware page for your system. Recall how the coverage graph on your main page looked before the signal strength dropped. If you touch the “Show position distribution for:” box at the top of the coverage graph you can select a different day on the drop down calendar. Select July 5th or earlier, there you can see you were receiving signals are received in the 150-200 mile range. Sometime on the 6th, your range dropped into the first zone, like the antenna or cable or the connection between the two developed a problem. Look for water damage at the cable connection as that is the most vulnerable point. Make sure the cable connection is tight. Maybe a storm and winds wiggled something. Water in the cable causes the signals to degrade. Could even be some critter decided to taste your cable insulation for their dinner. Do you have an different cable you can connect? even a shorter one with the dongle and raspberry pi hanging in the non-rain wind. Diagnosing problems like we see often is best solved by replacing cables or other parts one at a time and seeing what happens.
You install Graphs1090 as those will show you how the software and hardware from the dongle and Pi are processing data. Super useful diagnostic tool: Graphs for dump1090 -- my version with install script
Have some fun working out what is happening and might be handy to get the whole system down to your workbench so you can put the antenna near a window and sit next to your computer and see how things are working while you swap parts around. Best wishes and welcome to a fun hobby.