If you go to the OneNote.com website to download the OneNote installation, by default, the download button on the website is the 32-bit OneNote installation downloader.

If you want to download 64-bit OneNote. You need to click on the "Other download options" link.

Expand Hidden Content to find the 64-bit Free Download link.

You can see the expanded hidden content:

For the best compatibility, we recommend the 32-bit version. If you already have other 64-bit Office products installed, use the 64-bit version of OneNote.

Free Download >

In hidden content, we still see that Microsoft recommends: for best compatibility, we recommend using a 32-bit version of OneNote.