You're right, the missing SDK version was the reason that triggered the error when launching the app. Quinn, thanks a lot for your help!An error message like "Library rejected due to missing or outdated SDK version" instead of "code signing blocked mmap()" would have saved me a lot of time...Two months ago I was able to create a lib with valid SDK version using these clang calls:/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang++ \ -c \ -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk \ -mmacosx-version-min=10.13 \ -o test.o \ test.cpp /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang++ \ -Wl,-syslibroot,/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk \ -mmacosx-version-min=10.13 \ -dynamiclib \ -o TestLib \ test.oOn my current system (I guess there was an Xcode update in the meantime?) the test.o still has "sdk 10.15.4" set, but the linker (second clang call) drops the SDK version. To fix this, I have to pass "-isysroot ..." to the linker call. Or I have to set the SDKROOT environment variable, or I have to launch the build process with "xcrun --sdk macos ...".I've thought I can pass the SDK version as "syslibroot" to the linker, but maybe I'm wrong. I'm missing a good documentation how to build software on command line, without Xcode.

I'm building and testing the software with the latest macOS (10.15.4) running on the latest iMac, xCode is is up-to-date, too.

Disable Library Validation Entitlement: "the app may load arbitrary plug-ins or frameworks, without requiring code signing"... but all libs of my app bundle are code signed. I would like to know which unsigned lib triggers this problem.You're right, deployment of Qt applications on macOS is a pain. If I'm using the prebuilt libs provided by the Qt company everything works fine. If I'm building the Qt libraries on my own (which is required in my project...) I get the mmap code sign error. So I'm quite sure that there must be solution without disabling library validation.