I started a fresh clone of this and tried to use qt5-base but the runner reports:
Building package qt5-base[core]:x64-osx...
-- Figuring out qt target mkspec. Target arch x64
-- Target mkspec set to: macx-clang
-- Host mkspec not set. Qt's own buildsystem will try to figure out the host system
-- Downloading https://download.qt.io/official_releases/qt/5.15/5.15.2/submodules/qtbase-everywhere-src-5.15.2.tar.xz;https://mirrors.ocf.berkeley.edu/qt/official_releases/qt/5.15/5.15.2/submodules/qtbase-everywhere-src-5.15.2.tar.xz -> qtbase-everywhere-src-5.15.2.tar.xz...
-- Extracting source /Users/runner/work/SerialAudio/SerialAudio/vcpkg/downloads/qtbase-everywhere-src-5.15.2.tar.xz
-- Applying patch patches/winmain_pro.patch
-- Applying patch patches/windows_prf.patch
-- Applying patch patches/qt_app.patch
-- Applying patch patches/gui_configure.patch
-- Applying patch patches/icu.patch
-- Applying patch patches/xlib.patch
-- Applying patch patches/egl.patch
-- Applying patch patches/zstdd.patch
-- Applying patch patches/mysql_plugin_include.patch
-- Applying patch patches/mysql-configure.patch
-- Applying patch patches/Qt5BasicConfig.patch
-- Applying patch patches/Qt5PluginTarget.patch
-- Applying patch patches/create_cmake.patch
-- Applying patch patches/Qt5GuiConfigExtras.patch
-- Applying patch patches/limits_include.patch
-- Using source at /Users/runner/work/SerialAudio/SerialAudio/vcpkg/buildtrees/qt5-base/src/5.15.2-fa8de595e1.clean
xcodebuild: error: SDK "/Library/Developer/CommandLineTools/SDKs/MacOSX10.15.sdk" cannot be located.
xcrun: error: unable to lookup item 'SDKVersion' in SDK '/Library/Developer/CommandLineTools/SDKs/MacOSX10.15.sdk'
-- Detected OSX SDK Version:
CMake Error at ports/qt5-base/portfile.cmake:323 (string):
Error: string sub-command REGEX, mode MATCH needs at least 5 arguments total to