Outlook and Teams open links on Microsoft Edge
Stop Outlook and Teams from opening links in Edge regardless of your default browser: set the BrowserChoice registry value under Office\16.0\common\links.
Autodiscover Ignores Exchange Online? Check the Registry
Outlook asks for Office 365 credentials while the mailbox is still on Exchange on-premises: set ExcludeExplicitO365Endpoint under the Autodiscover key.