Using GCC10 with Qt on KDE Neon 18

I would like to play around with some very new C++20 features. Some of them are supported by GCC10 only. Unfortunately the most current release is GCC9.3 so I need to use the unreleased version of GCC10.

I did the following to install it:

sudo add-apt-repository ppa:ubuntu-toolchain-r/testsudo apt install gcc-10 g++-10

This worked fine. However I am unable to make it the default compiler. As usual I tried:

sudo update-alternatives --config gcc

This says there would be no alternatives. Why?