iCloud for Outlook Incorrect Username or Password

Eventually realised this was due to a problem with the “Calendars and Contacts” option preventing the iCloud sign-in from completing. Resolved the issue by deselecting all the options which allowed the iCloud sign in to complete. Then one by one successfully enabled “Passwords and Keychain”, “Bookmarks” and “iCloud Drive”. I then found another thread suggesting the “Calendars and Contacts” issue was because classic Outlook needs a .pst file (not imap .ost) set as the default data file for the process to complete. The problem was fully resolved by creating a .pst file in Outlook and setting it as the default data file.