You access dataloader.io from MuleSoft, click on Login with Salesforce, select (or not) your custom domain and Environment, click on the login button, and then dataloader.io from MuleSoft logs you in as a user that was used before, without asking for a username and password.
You don't find any way to log in to a different account.
This issue happens because dataloader.io from MuleSoft uses an active Salesforce session.
To solve this issue you have more than one option:
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