With new new 1.8.13 version of IDE I cannot compile a sketch, probably due to the lack of the program avr-g++ (see the following error message!) :
Arduino: 1.8.13 (Mac OS X), Board: "Arduino Uno"
....
....
/Users/Ernst/Library/Arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/bin/avr-g++: no such file or directory
Fehler beim Kompilieren für das Board Arduino Uno.
This error indicates something has gone wrong with the Arduino AVR Boards platform installation via Boards Manager. The solution is to remove the installed packages. Be aware this will remove any boards you have installed via Boards Manager:
(In the Arduino IDE) File > Preferences
Click the link on the line following "More preferences can be edited directly in the file". This will open the Arduino15 (or similar name depending on OS) folder.
Delete all files and folders under the Arduino15 folder except for preferences.txt. Please be very careful when deleting things from your computer. When in doubt, back up!
Restart the Arduino IDE
Verify that you can now use your board before reinstalling any packages via Boards Manager.