It's frustrating because usually Boards Manager works fine but every so often it glitches and it's not designed well to gracefully recover from this.
Try this:
- Close all Arduino IDE windows.
- Delete C:\Users\Albnar\AppData\Local\Arduino15\packages\arduino\tools\avrdude\6.3.0-arduino9. Please be very careful when deleting things from your computer. When in doubt back up!
- Start the Arduino IDE.
- Try uploading again.
Deleting the incompletely installed avrdude will force the Arduino IDE to use the version of the tool which comes with the Arduino IDE, as it was doing before you updated to Arduino AVR Boards 1.6.21.
albnar:
I got a new avrdude.conf from https://github.com/arduino/Arduino/blob/master/hardware/arduino/avr/bootloaders/gemma/avrdude.conf
That avrdude.conf is specifically for the ATtiny85-based Gemma board so it is not necessarily a direct replacement for the file that was not installed during the problematic update.