@WhitesLove I didn't say you need to remove all your mods and custom content. What I said was you need to test it and remove any items that cause spikes in RAM use, or crashing, or any other performance issues. This is just good practice and all the more necessary with a 32-bit app.
I don't know what 4 GB patch you're referencing, but if you mean the kind of patch that makes 32-bit apps large-address aware, Sims 3 received that patch in 2010. It's already running at the mathematical limit for an application that uses 32-bit addresses.
And no, it's not possible to use any aspect of the 64-bit Mac version in Windows. In addition to being written for a different OS, the Mac version uses an entirely different graphical API (Metal) that doesn't exist in Windows. It would probably be more efficient to start fresh with a Windows-only update than to try to translate the Mac version for Windows.
This is all a moot point though. As far as any of us knows, EA has absolutely no interest in updating the Windows version, which still runs fine, as opposed to the 32-bit Mac version which wouldn't run at all in the last four versions of macOS.
