Edge Profiles - launch selected profile.

If you have multiple Edge profiles, it may be useful to launch directly into your selected profile.  To do this, set your default profile i.e. not the last used, and then create shortcuts to launch edge with your various other profiles.

By default, Edge 84.0.522.52 will launch into the last used profile.  It does not seem possible to override this behaviour and fix the default permanently.  Using this settings page to fix the default profile edge://settings/profiles/multiProfileSettings only achieves exactly what it describes. i.e. controls the profile used by links from external apps such as email.
"By default, Microsoft Edge uses the last used profile to open links in email or other applications. If you have other profiles in Microsoft Edge, you can choose which one to use."

It does not fix the default and stop it being changed by closing Edge when a different profile is active.

Edge stores the user profile in folders under %LOCALAPPDATA%\Microsoft\Edge\User Data .
Default is the first profile with additional profiles stored under folders called Profile 1, Profile 2 and so on.

It is possible to specify the profile required at launch with a command line and parameter of
"C:\Program Files (x86)\Microsoft\Edge\Application\msedge.exe" --profile-directory="Default"
or
"C:\Program Files (x86)\Microsoft\Edge\Application\msedge.exe" --profile-directory="Profile 1"
etc

Edge Profile Picture.png files in the profile folder may contain a profile picture if one exists providing one method of identifying the Profile.

The Edge shortcut in the start menu will always launch with the profile that was active when Edge was last closed.  This could could be the profile in Profile 1 if that was the active profile when Edge was last closed.  The profile in the Default is not necessarily the profile that will be used when the Edge start menu shortcut is selected.

Set a file association back to Choose a default

Backup the reg key
[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts\.<ext>]

then delete it.

The file assocation in Settings_Apps_Default Apps_Choose default applications by file type will revert to Choose a default.

Edge Microsoft Account Sign In Loop

Edge may require some Microsoft sites to be added specifically allowed to store cookies.  Addition of the sites specified in the article below may prevent a sign in looping effect where you are constantly prompted to sign in, even after submitting credentials.

https://docs.microsoft.com/en-us/microsoftteams/troubleshoot/teams-sign-in/sign-in-loop