The Google Drive App (from which the Google Drive Widget is derived) supports login to Google Drive with a single account.
If you wish to sign-in to Google Drive with multiple accounts, you'll need to use a suitable third-party File Manager App. While this offers a workaround for multiple accounts, you may not be able to use Widgets to do so.
Of suitable File Manager Apps that support simultaneous login to multiple Google Drive accounts, perhaps consider Stratopherix FileBrowser - Document Manager, or its “pro version” FileBrowser Professional:
https://apps.apple.com/app/filebrowser-professional/id854618029
https://apps.apple.com/app/filebrowser-document-manager/id364738545
You might review the extensive online Manual and help files to determine suitability for your needs.
https://www.stratospherix.com/products/filebrowserprofessional/filebrowser-professional-user-guide.php