Configuring preferences and options in Outlook.com
Mark's email link here has the resolution of O365 in a web browser.
One additional note: You MUST use this method if your org also uses OneDrive Cloud and it's lock down. This option allows you to choose the invite file from OneDrive.
What a stupid, convoluted mess. Maybe one of the worst app design features I have experienced in the 30 year of MS "wizardry".