After the migration from SharePoint 2013 to SharePoint 2019, the login method for users changes from Shibboleth to NTLM.
After calling up the SharePoint website, a login dialog opens to request the login data. This dialog does not appear on the web page itself, but is displayed by the web browser used. For a successful login you need as
Firefox, Chrome etc.
Microsoft Edge (Windows)
If you want to open a document from SharePoint in Microsoft Office, you must also log in to the Office program. For a successful login you need as