I have Visual Studio build Tools 2017 installed on my PC.
Is it OK to uninstall Visual Studio Build Tools 2017 after installing the 2019 version? Is there software that cannot be built by 2019 version and instead requires 2017 to be built?
I am using Visual Studio Community 2019.
They are a separate set of tools, therefore you can safely remove the old building tools without affecting the stability of Visual Studio 2019.
However, MSbuild 16 shipped with Visual Studio 2019 introduces new features and some breaking changes which could result in compatibility problems (here the main announcement).
In case you run into them, you can always install the old Visual Studio 2017 Build Tools in Visual Studio 2019 by selecting the old tools via individual component. Then, you can change the toolset of the offending project by specifying the version you need as stated in msbuild documentation.