Who can solve this ?  

It only uses VisibleClasses and Classes IIRC.

Don't forget to run 0ad/source/tools/spirv/get-nightly-shaders.sh if you want to use Vulkan.

Be sure to follow https://gitea.wildfiregames.com/0ad/0ad/wiki/BuildInstructions tl;dr have all dependencys run 0ad/libraries/build-source-libs.sh run 0ad/build/workspaces/update-workspaces.sh run make -j5 in the folder 0ad/build/workspaces/gcc/

As I see it, you are right. I downloaded and installed the branch from git with  git clone --single-branch --branch release-a27.1 https://gitea.wildfiregames.com/0ad/0ad.git But you can also download from https://releases.wildfiregames.com/ 27.1 is from 14.07. so the distros may need some till it lands in their repos.

They are quite a lot slower than cav.

Hello, I just tried to download the latest alpha version from the official web page for Linux, but it seems there is no link or something and had to install it from the Software Manager of my distro, but it is not the latest alpha, as it says 0.27.0 in version.