can't do on osx without reformat if i'm recalling correctly

APFS filesystem has volumes that share shape with Macintosh HD. You can create a separate encrypted case sensitive volume called Development

that's like using a nuke to hammer a nail.

It really isn’t. APFS has excellent support for logical volumes, and it’s barely any harder than creating a new folder.

(Each volume can also use an extra encryption layer if you want, which can be super useful.)