Tried installing the pixel thermometer on a pixel 8 pro from Aurora Store. Received the following error:

INSTALL_FAILED_SESSION_INVALID: Only the first-party package source and shell are allowed to install com.google.android.apps.pixel.health

Any idea what that's about?

    I can't explain exactly why you can't use Aurora Store but you can install it via the App Store that comes with GrapheneOS.

    You can't install it using Aurora, you can only install it via GrapheneOS's App Store app.