That indicates the problem is definitely the second bullet point in Problems installing Opus.
Windows is incorrectly telling the installer that your system is 32-bit when it is 64-bit.
The known solutions are to either install from a fresh Windows account (then switch back to your main account afterwards), or to reinstall Windows.
It is not Opus or the Opus installer that has gone wrong here, since it affects older versions of the installer which used to work fine on the exact same systems. Something has gone wrong with the Windows user profile or Windows install, or there is a piece of software that's breaking things and only run under the normal account.