That is a reasonable approach, one of the 2 MacOS fuse implementations uses NFS.
I've never written an SMB server, but I assume it is a lot more complicated than using WinFsp or Fuse.
WSL 2 uses the 9P network filesystem to share files between Linux & Windows. Supposedly this is a simple protocol to implement. I've searched, but can't find any documentation on using 9P without WSL.
Cryptomator suggests WinFSP for its Windows installation, MacFUSE for Intel Macs, and FUSE-T (the NFS FUSE implementation) for Apple silicon Macs. I've used all of them, and I've also used Dokan with encfs.
Both OSes treat network filesystems differently from local disks. The FUSE-T implementation is very speedy, but it shows up in the finder as a connection to "localhost", not as a properly named mount. In addition, macOS creates .DS_Store files on network drives by default (there is a setting you can change from the CLI to prevent this). On Windows, the filesystems can be mounted as local drives or network drives. When mounted as network drives, they can have issues with indexing and trust. All-in-all, drives you expect to function as local drives work best when they're actually local device filesystems and not network mounts.
I've never written an SMB server, but I assume it is a lot more complicated than using WinFsp or Fuse.
WSL 2 uses the 9P network filesystem to share files between Linux & Windows. Supposedly this is a simple protocol to implement. I've searched, but can't find any documentation on using 9P without WSL.