I'm using an open source library (libturbojpeg), and the library has been built more or less the same for years. The 2.0.2 version links fine for Device and Simulator in both Xcode 11.3 and 11.4.1-beta.
But newer releases generate warnings in 11.3 when using 2.0.3 or newer (for example):
ld: warning: building for iOS Simulator, but linking in object file (/Volumes/Data/git/PhotoScrollerSwiftPackage/Libraries/libturbojpeg.a(jdapimin.c.o)) built for macOS
Worse yet, in Xcode 11.4.1-beta, those turn into hard errors and the build fails:
error: Building for iOS Simulator, but the linked library '208libturbojpeg.a' was built for macOS + iOS. (in target 'LTJTest' from project 'LTJTest')