For the handful of composers who need a reliable way to make boxed notation:
I made an admittedly long-winded tutorial on one of my aleatoric workflows. The main goals were to make a box that would be attached to the rhythmic grid, easy to copy/paste, and that would propagate to parts with minimal adjustment. The main drawback is this method requires the line editor in version 3.5 but really, the update is worth it for granting access to Big Mango.
The TL;DR is you make a custom line with long, inward-facing hooks. Oh and I’ve provided timestamps in the video description for those of you who are pressed for time. This way you can navigate straight to the point, circumventing my babbling.