In this case, Dark Reader would darken over Bitwarden's password popup (the one that asks if you want to save the login info).
Steps:
- Go to extension settings (the browser settings page, no in Dark Reader)
- Find the extension you want to whitelist
- In Edge at least, it shows a long ID, copy it
Now in Dark Reader settings (you may need to enable the new UI, v5 it's called?)
- Settings -> Site list
- Add one with this format (no quotes): "extension://(the id you copied earlier)"