It turns out that 32-bits for Windows was discontinued with Roon 2.0:
Unfortunately, the documentation wasn’t updated accordingly, where it says,
Windows users will still be able to run Roon as a 32-bit app, but most users will want to switch over to 64-bit versions of Roon and RoonServer, especially with collections over 100,000 tracks.
You could still use Roon 1.8, for which installers are still available. However, you would be better off upgrading your Windows to 64-bits. This is the better approach for Roon and everything else. Roon 1.8 is not being maintained anymore.