Previously you could install and update the toolchain for arm cortex R and M cpu's using apt by just adding the ppa and doing a normal apt install, but that ended for whatever reason.

Here's the way to "install" the latest versions on ubuntu 20.04. If you have the old one installed, remove that first using:

sudo apt remove gcc-arm-embedded

Go to arm's developer tools and download the one for your arch.

Extract it to your folder of choice. Edit your .bashrc file and add the bin folder to the path variable as shown below.

# >>> ARM >>>
export PATH="$PATH:/home/user/path/to/gcc-arm-none-eabi-10-2020-q4-major/bin/"
# <<< ARM <<<

Close and re-open your terminal(s). Now it should use the new version:

$ arm-none-eabi-gdb firmware.elf --ex 'target remote localhost:3333'
GNU gdb (GNU Arm Embedded Toolchain 10-2020-q4-major) 10.1.90.20201028-git
Copyright (C) 2020 Free Software Foundation, Inc.

Every time they do a new release, repeat...