New in Microsoft Edge Version 82.0.421.0 (Official build) canary (64-bit)
Reason for doing it is more about privacy and stopping fingerprinting.
edge://flags/
Freeze User-Agent request header
Set the User-Agent request header to a static string that conforms to the current User-Agent string format but only reveals desktop vs Android and if the 'mobile' flag is set – Mac, Windows
#freeze-user-agent
to be more effective, also enable this flag:
Reduce default 'referer' header granularity
If a page hasn't set an explicit referrer policy, setting this flag will reduce the amount of information in the 'referer' header for cross-origin requests. – Mac, Windows
#reduced-referrer-granularity
More info:
https://www.chromestatus.com/feature/5704553745874944
https://css-tricks.com/freezing-user-agent-strings/
