BT Webmail is working now.
This morning BT Webmail was taking a long time to open in Microsoft Edge.
Microsoft Outlook was still able to access Btinternet.
I deleted all my history and reset Microsoft Edge and it is responsive again.
Microsoft Edge is up to date.
Version 140.0.3485.54 (Official build) (64-bit)
I noticed today it now defaults to the setting that works.