MPLAB X is the standard choice for modern AVR development. It features cross-platform compatibility for Windows, macOS, and Linux, and integrates seamlessly with the XC8 compiler. To help find the right version, let me know:
To download AVR Studio 5.1, follow these steps: avr studio 51 download extra quality
If you are trying to enable Deep Physical debugging on an AVR Dragon or similar hardware: MPLAB X is the standard choice for modern AVR development