Summary
In order to tighten our security, Microsoft have recommended that SharePoint online is restricted to login using Modern Authentication. This change will have very little impact. Most modern web browsers will allow you to access using Modern authentication.
How to recognise if you are using Modern Authentication:
If the following login prompt is similar to what you see when you try to login to SharePoint online, then you are using a browser that supports Modern Authentication. If it is very different, you may need to upgrade, or use another browser to access Microsoft SharePoint.
There will be no downtime during this time window.
Change – 17982