sudo apt install build-essential manpages-dev software-properties-common
sudo add-apt-repository ppa:ubuntu-toolchain-r/test
sudo apt update && sudo apt install gcc-11 g++-11

Then use update-alternatives to set default gcc...

sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-9 90 --slave /usr/bin/g++ g++ /usr/bin/g++-9 --slave /usr/bin/gcov gcov /usr/bin/gcov-9 --slave /usr/bin/gcc-ar gcc-ar /usr/bin/gcc-ar-9 --slave /usr/bin/gcc-ranlib gcc-ranlib /usr/bin/gcc-ranlib-9  --slave /usr/bin/cpp cpp /usr/bin/cpp-9 && \

sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-11 110 --slave /usr/bin/g++ g++ /usr/bin/g++-11 --slave /usr/bin/gcov gcov /usr/bin/gcov-11 --slave /usr/bin/gcc-ar gcc-ar /usr/bin/gcc-ar-11 --slave /usr/bin/gcc-ranlib gcc-ranlib /usr/bin/gcc-ranlib-11  --slave /usr/bin/cpp cpp /usr/bin/cpp-11;

To sample check settings to see which gcc is default you can run the following, if they show correct resuslts then the rest are fine...

gcc --version;g++ --version;gcov --version;

To reconfigure to any previous gcc version...

sudo update-alternatives --config gcc

You can do this on any version of ubuntu,... enjoy!

Here are my 6 different gcc's living side by side with the default being gcc-11:

$ sudo update-alternatives --config gcc
There are 6 choices for the alternative gcc (providing /usr/bin/gcc).

  Selection    Path             Priority   Status
------------------------------------------------------------
* 0            /usr/bin/gcc-11   1010      auto mode
  1            /usr/bin/gcc-10   1000      manual mode
  2            /usr/bin/gcc-11   1010      manual mode
  3            /usr/bin/gcc-5    40        manual mode
  4            /usr/bin/gcc-7    700       manual mode
  5            /usr/bin/gcc-8    800       manual mode
  6            /usr/bin/gcc-9    900       manual mode

Press <enter> to keep the current choice[*], or type selection number: