Hi Mark,
You've found a weird bug. We don't deny any features in the sandbox. Curious, I installed the sandbox locally (on main, not on the latest release, though at the moment they're the same commit) and was unable to reproduce your issue (I went to Extend and installed the Book module with no issue).
If you're getting a fully loaded Drupal page with a header bar etc. that says Access Denied, then I'm completely baffled. I can think of a few ways to do that but you'd have to go out of your way.
If you're getting a white screen with a stark error message, then it might be a fault of one of our modules, and the tools below might help:
My main debugging tool is the Drupal log, so if you can access
http://islandora.io/admin/reports/dblog in your browser it might have more info. If access is denied, you can dig into the logs by going in the docker container. Most folks here use `docker compose exec` with a million flags that I forget, so I use Docker Desktop, find the Drupal container (called something like "sandbox-drupal-1") and click "Exec" to open a shell. From the home directory I can run the command `drush ws` to show the logs, `drush ws --extended` to show more detail.
And failing that, the apache logs. But I'm not sure that's relevant because you mentioned seeing "Access Denied".
The Sandbox
should work as you're intending it to, so I'm happy to continue debugging with you. But you could try one of our other installation methods.
Isle Site Template is closest to the Sandbox, and only requires ~5 more copy-paste commands to get it running.
ISLE-DC is another option, which does a lot more scaffolding (such as bind-mounting a codebase folder so you can use an IDE on local files).
Feel free to join us on Slack too!
-Rosie