Thanks for helping out.
I deleted the two lines from my PATH, and will use the VS command prompt you suggested. Does that mean, I should remove the following commands from my installation routine?

set CMAKE_GENERATOR=Visual Studio 16 2019

set CMAKE_GENERATOR_TOOLSET_VERSION=14.28

"C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Auxiliary\Build\vcvarsall.bat" x64 -vcvars_ver=%CMAKE_GENERATOR_TOOLSET_VERSION%

set CUDAHOSTCXX=C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.28.29910\bin\HostX64\x64\cl.exe

Another question:
The issue that CUDA cannot find Visual Studio remains, even though I have

MSVC v142 - VS 2019 C++-x64/x86-Buildtools (v14.28)

installed (I installed Visual Studio and all components using this previously mentioned file)
Should I just reinstall it using VS Community (which seemed to work), and install the newest MSVC and SDK?
And if so, would you suggest VS Community 16.8.5 - matching the current Buildtools version - or the latest?