The solution of the downloaded framework has four supported platforms: ARM and x86 for 32-bit builds, ARM64 and x64 for 64-bit builds. Where ARM and ARM64 platforms are used for Android projects only. It also has several configurations. They are Debug, DebugRT, Release, ReleaseRT. Configurations without RT produce static libraries with static runtime library linking. Configurations with RT produces static libraries with linking runtime library in DLL. Use RT configurations to build Form Builder and for building your own packages. When developing applications use non-RT configurations.
For the Linux projects you will also need to setup connection to your Linux for remote building. Use Linux projects only if you are going to implement platform dependend classes by your own because there are no such implementation out of box yet.
Anyway you are free to add your own configuration for your applications. Just don't forget the framework core and Standard package configuration should be compatible with build configuration of your application(pay attention on using runtime libraries, platform toolset, and SDK version).
Build solution in DebugRT or ReleaseRT to produce Form Builder executable files. They will be placed in the x86 or x64 directory(depending on selected platform) inside the installation folder into DebugRT or ReleaseRT subdirectories(depending on selected configuration).