Why is Microsoft Edge autofilling disabled fields on my Webform CiviCRM?
I found the answer in a post on the Miscrosoft developer forum:
https://developer.microsoft.com/en-us/microsoft-edge/platform/issues/9847360/

Some of the 'highlights':

From Microsoft:
“In IE11 and Edge, we made the decision to ignore autocomplete=off”

From a developer:
WHAT !!! ???
That’s why we are receiving so many UI complaints recently. This is a terrible decision Microsoft.
Please STOP breaking Edge by NOT supporting standard HTML correctly.
Edge should honor the autocomplete="off" tag.

And from another one:
“By Design” doesn’t mean that the functionality is correct. I’m struggling with a complex web form that is auto-populating the wrong values into some text fields in Edge browser"