Getting started with sys-gui

I just installed Qubes 4.1 and enabled sys-gui after the provisioning on my previous installation corrupted. I am running into a number of issues with sys-gui.

How do I mount external disks to VMs? They appear to be completely inaccessible within sys-gui. The disk applet in the task bar does not open when clicked like it does in dom0, and the disks do not appear in nautilus or from the terminal.

Any type of qvm-* command seems to fail from within sys-gui, producing the error eg “qvm-clone: error: Service call error: Request refused”.

I also cannot use “qvm-run vm-name xterm” as it fails with an error that ends with “BrokenPipeError: [Errno 32] Broken pipe”. I also get an error in the top-right corner that says “Denied qubes.VMShell from sys-gui to fedora-34”.
It seems like I probably need the dom0 terminal, but I can’t figure out how to open that in sys-gui.