If you don't want Simplified to have direct access to your documents, disable the Google Drive integration in just a couple of steps:
1- Click Settings on the left-side toolbar.
2- Choose Connected Apps.
3- Click on the three dots of the connected account and then select the Disconnect option.
Note: In this case, once Google Drive is disconnected, you will be able to use your assets and files by simply dragging them onto an artboard.