Okay, thank you!
Is it possible that the docs on this are out of date? Link: How to use disposables | Qubes OS
Here’s the relevant text:
Starting an arbitrary program in a disposable from an app qube
Sometimes it can be useful to start an arbitrary program in a disposable. The disposable will stay running so long as the process which started the disposable has not exited. Some applications, such as GNOME Terminal, do not wait for the application to close before the process exits (details here). Starting an arbitrary program can be done from an app qube by running
[user@vault ~]$ qvm-run '@dispvm' xterm