Regarding keyboard shortcuts, it will feel like logging onto a Remote Desktop session - you would press Control+Alt+Break (Pause) key to switch between host (the computer you are using) and guest (sandboxed environment). The way I run NVDA (or for that matter, any screen reader other than Narrator) inside Windows Sandbox is:
- On the host computer, prepare the screen reader files - NVDA installer or a portable copy of NVDA.
- Copy the screen reader file(s) to the clipboard.
- Go to Windows Sandbox and switch to the guest environment.
- Open a folder location (say, Documents). The easiest way is typing the name of the folder from Run dialog.
- When the desired folder opens in the guest environment, paste the just copied scren reader file(s).
- Because it will take time for files to be copied (especially if you are copying a folder containing portable NVDA files), switch out of sandboxed environment, then use Windows OCR (NVDA+R) to recognize what Windows Sandbox is displaying.
- Once the copy operation is complete, switch back to the sandboxed environment, locate NVDA executable and run it.
You can also do all these with Narrator on - just before opening the folder in the guest environment (just after performing step 3), press Control+Windows+Enter while switched to the guest environment to start Narrator inside the sandbox. When NVDA starts, close Narrator.
I belive Windows Sandbox was covered somewhat on WinAccess forum (may need to check the archive for that one).