Easy now, apparently:
- In Google Authenticator, click the hamburger at top left, then choose “Transfer Accounts”
- Click “Export Accounts”
- Select accounts to export (Should default to all). Click “Next”
- You’ll be shown one or more screenshots (depending on how many codes you have). Take a screenshot of each QR code. In my case I’m on an iPhone, so they are saved to Photos.
- Easiest: Open photos on another device
- In Bitwarden Authenticator, click “Settings” at bottom right, then “Import”
- Click on “Authenticator Export (JSON)” to reveal other options.
- From the list, choose “Google Authenticator”, then click “Import Items”
- Scan the QR codes until all items imported.