I ran a similar setup for a few years. Trying to set Zotero on both Mac and Windows to point to the same database file caused lots of data corruption problems and headaches due to both the Mac and Windows systems interacting with the file at the same time (even when I was very careful to never open Zotero on both sides at once). I would recommend just setting up Zotero to keep two separate databases, one on each system, and use Zotero Sync to keep them up to date. For attachment files, you can set a symbolic link to connect the two storage folders (https://www.zotero.org/support/sync), or, easier, you could just set one or both Zotero apps to only download attachment files as needed (https://www.zotero.org/support/preferences/sync).