You absolutely can have both and x64 architecture will be prioritized if the code was built for AnyCPU. You should have this is mind for the following dev story :

I just experienced a lot of debugging on my side relevant to this question. .NET runtimes can make a difference whether they were installed for x64 or x86 for C++/CLI applications.

For days I looked around on why my program was working on machines of programmers but not on users' machines, and the cause was found to be that Visual Studio downloads both runtimes, but an install via the .NET website only downloads one, and most of the time you will use x64. But for my case, I needed x86 as the library I was creating was to be used for legacy x86 code.

Note : the dotnet command will most likely only show you x64 installs, as the PATH probably prioritize x64 paths.