Getting the error: 'Your browser is not supported or up-to-date. Try updating it, or else download and install the latest version of Microsoft Edge.'
The issue is due to the Multi-Factor Authentication. The user needs to update their mobile number in relation to their O365 MFA settings, they can do it by:
Login to https://portal.office.com
Select your profile icon in the top right and select 'View Account'.
Select 'Security Info'
Select 'Change' or 'Add sign-in Method'
The user should be able to manage their own Security settings.
Locate phone and then click 'Change'.
Once your mobile number has updated, this should work as normal.