Just found out that the identifier is right in the AUv3’s plist file (ch.toguaudioline.talunolxv2.talunolxv2AUv3), but it does not mach the one in the General tab in XCode (ch.toguaudioline.talunolxv2.toguaudioline.talunolxv2AUv3).
The contents of the plist file is generated by the same C++ code that is linked in both Projucer and juceaide (the utility executable that is built and run when using JUCE 6’s CMake support). That’s why there is no difference there.
However, the identifier set on the AUv3 target is computed by extras/Build/CMake/JUCEUtils.cmake and I think there is a bug there. Applying the following patch should fix it: