It is extremely flaky on GrapheneOS, at least on my Pixel 8 Pro. Just typing Ctrl-D to exit will corrupt it, requiring a full reinstallation of the Debian VM

The built-in terminal app seems to be similarly flaky on my Pixel 8. Also, the kernel it boots into is really stripped down, and it lacks a ton of essential features. I was not able to install VirtualHere client to pass through USB devices, and there's no built-in functionality. There's also no way to open it full-screen on the Pixel 8's DP-over-USB-C desktop mode. Hopefully it continues to improve, but it seems like Google is more into extracting value than they are improving their products at this point.

Control-D works fine for me. It just terminates the VM and you can restart.