The LLVM bash script to update the apt repo's doesn't work on KDE neon.
It just says
Distribution 'Neon' in version '20.04' is not supported by this script (Neon_20.04). so here's how to manually update to LLVM-13 or whatever verison.
If it's the first time add the key as described in https://apt.llvm.org/
wget -O - https://apt.llvm.org/llvm-snapshot.gpg.key | apt-key add -
Create a file in
llvm-toolchain-focal-13.list with the following:
deb http://apt.llvm.org/focal/ llvm-toolchain-focal-13 main
# deb-src http://apt.llvm.org/focal/ llvm-toolchain-focal-13 main
If you're on a different distro change focal and the version as needed. If you want the source repos uncomment the deb-src file.
sudo apt update and install
sudo apt install clang-13 lldb-13 lld-13 clangd-13
Hope it helps someone.