avr-gcc version: won't update from 5.4 to 9.2

I am trying to run compile some arduino code in my linux terminal and keep coming up with a problem, and I believe the issue is my avr-gcc version - when I run

avr-gcc --version

I get this:

avr-gcc (GCC) 5.4.0

But my friend, who is doing a similar project, has avr-gcc version 9.2 on his computer. When we try and compile code on mine, it won't run because the features are too new for my avr-gcc compiler.

Every time I try to simply update using the terminal, it won't work:

$ sudo apt-get install avr-gccReading package lists... DoneBuilding dependency tree       Reading state information... DoneE: Unable to locate package avr-gcc

When I delete avr-gcc and re-download it, it just comes up with 5.4 again. I've looked for a simple download link (like I found this one for Windows https://blog.zakkemble.net/avr-gcc-builds/), but can't find any. Any ideas?