Figured out how to apply any arbitrary SF Symbol to a folder in Tahoe.

xattr -w 'com.apple.icon.folder#S' '{"sym":"camera.viewfinder"}' some/folder/here

It also works with private symbol names!

@samhenrigold this seems far too complicated than it ought to be. then again, in windows you need icons in a ICO or DLL (or EXE, or anything else that can hold icons in that format really) to use them as custom icons for folders or shortcuts
Furbland's Very Cool Mastodon™, in macOS you could also set a custom .icns for a folder or a disk since about forever