When trying to build purpose in a minimal container, this fails since KAccountsConfig.cmake ist not found. This file is part of kaccounts-integration, which is not part of KF5. Please resolve this, as this might lead to circular dependencies between packages being part of KF5 and packages not part of KF5.
Purpose is a tier-3 Framework, and as such can depend on other packages, even if they're not part of KF. See https://api.kde.org/frameworks/index.html