the v3 migration docs state that For example, if you created a home homes/x86_64-linux/jake/default.nix, the home will be included for every x86_64-linux machine and will be exported on your Flake as homeConfigurations."jake@x86_64-linux".

but the generated homeConfiguration will actually be named only "jake"

that becomes a problem as soon as you try to create a target wide home config for more than one target as only the first one ( or only one, can't really tell if it's the first one ) seems to be build

in my exact case I defined a target wide home config for both x86_64-linux and aarch64-linux and while the x86_64-linux config kept building just fine the aarch64-linux one failed, not being able to find the defined home-manager user
my homeConfigurations included only one config with the plain name, no @<target>