So what you're looking for, simply, is a DMS (Document Management System) allowing you to save filters for common search files using tags, filters,
Created Dates and other friendly tags- so some sort of Metadata Editor may also be required.
For the Windows portion, I would suggest XYPlorer, however it fails to meet the OSX requirement. If this was of use, you can see my answer here on the product.
What I personally do, is operate my own local gallery via the LAN (use your NAS as the destination. A rather helpful guide on how to perform this can be found here, but this isn't all you'll need. This topic requires a rather technical approach.
This is a command line tool capable of editing metadata on files. The descriptor is as follows:
Exiv2 is a Cross-platform C++ library and a command line utility to
manage image metadata. It provides fast and easy read and write access
to the Exif, IPTC and XMP metadata and the ICC Profile embedded within
digital images in various formats. Exiv2 is available as free software
and is used in many projects including KDE and Gnome Desktops as well
as many applications including GIMP, darktable, shotwell, GwenView and
Of course, this too will require some CLI (Co-mmand Line Interface). A great guide can be found here. For example, adding a meta-tag of "
mytag", you would need to exucute the following command:
exiv2.exe -M "add Iptc.Application2.Keywords String mytag" myphoto.JPG
This tool is considered a more stable replacement to EXIFutils, which has been discontinued.
I assume accessing the NAS on OSX and Windows is simple enough (I think OSX uses
smb://IP/SHARE/...right?) so all we need to do now is ensure when a file is added, moved, or renamed the metadata is updated.
If you enable Bash on Windows 10 and have an admin account on OSX you could create a CRON Job to identify files with no specific tags/metadata. Assumptions are made and are just "food for thought" though... ;)