Hide Edge v149 forced rounded corners. Additionally hide red dot on profile icon too.

hide-edge-rounded-corners.ps1

# This script must be run as Administrator to update some shortcut paths. Checking it first...
$IsAdmin = ([Security.Principal.WindowsPrincipal] [Security.Principal.WindowsIdentity]::GetCurrent()).IsInRole(
    [Security.Principal.WindowsBuiltInRole]::Administrator
)
if (-not $IsAdmin) {
    Write-Host "Not running as Administrator. Some shortcuts may fail to update." -ForegroundColor Yellow
    Write-Host ""
}

# This is your Edge path, it should be installed here (if you're on Stable channel).
$EdgePaths = "${env:ProgramFiles(x86)}\Microsoft\Edge\Application\msedge.exe"

do {
    Write-Host "1. Old workaround (msFeatureGroupNewLookAndFeelHoldout)"
    Write-Host "2. New workaround (msForceNoRoundedCornerAndMargin)"
    Write-Host "3. Restore to default"
    $Choice = Read-Host "`nEnter choice"

    if ($Choice -eq "1") {
        # msFeatureGroupNewLookAndFeelHoldout is an older/broader workaround revert that ugly rounded corner.
        # msShowSignInIndicator is to hide the red dot on the profile icon if you wish to not sign in.
        $Options = '--disable-features="msShowSignInIndicator,msFeatureGroupNewLookAndFeelHoldout"'
    }
    elseif ($Choice -eq "2") {
        # msForceNoRoundedCornerAndMargin is a newer option for removing rounded corners.
        # Use this instead if msFeatureGroupNewLookAndFeelHoldout stops working or affects other UI.
        $Options = '--enable-features="msForceNoRoundedCornerAndMargin" --disable-features="msShowSignInIndicator"'
    }
    elseif ($Choice -eq "3") {
        # Restore default shortcut behavior by removing all arguments.
        $Options = ''
    }
    else {
        Write-Host "Invalid choice. Please try again.`n" -ForegroundColor Red
    }
} until ($Choice -in @("1", "2", "3"))

# Use WScript (a script host) to modify shortcuts
$Shell = New-Object -ComObject WScript.Shell

# This is your Edge possible shortcut paths.
# If you have shortcuts placed anywhere else, put them in this list as well.
$ShortcutPaths = @(
    "$env:Public\Desktop\Microsoft Edge.lnk",
    "$env:UserProfile\Desktop\Microsoft Edge.lnk",
    "$env:ProgramData\Microsoft\Windows\Start Menu\Programs\Microsoft Edge.lnk",
    "$env:AppData\Microsoft\Windows\Start Menu\Programs\Microsoft Edge.lnk",
    "$env:AppData\Microsoft\Internet Explorer\Quick Launch\Microsoft Edge.lnk",
    "$env:AppData\Microsoft\Internet Explorer\Quick Launch\User Pinned\StartMenu\Microsoft Edge.lnk",
    "$env:AppData\Microsoft\Internet Explorer\Quick Launch\User Pinned\TaskBar\Microsoft Edge.lnk"
)

foreach ($ShortcutPath in $ShortcutPaths) {
    if (Test-Path -LiteralPath $ShortcutPath) {
        try {
            $Shortcut = $Shell.CreateShortcut($ShortcutPath)
            $Shortcut.TargetPath = $EdgePaths
            $Shortcut.Arguments = $Options
            $Shortcut.WorkingDirectory = Split-Path $EdgePaths -Parent
            $Shortcut.IconLocation = "$EdgePaths,0"
            $Shortcut.Save()

            Write-Host "Recreated: $ShortcutPath" -ForegroundColor Green
        }
        catch {
            Write-Host "Failed to update: $ShortcutPath. Error: $($_.Exception.Message)" -ForegroundColor Red
        }
    }
    else {
        Write-Host "Skipped, not found: $ShortcutPath" -ForegroundColor Yellow
    }
}

Write-Host "`nPress any key to exit..."
$Host.UI.RawUI.ReadKey("NoEcho,IncludeKeyDown") | Out-Null
powershell -NoExit -NoLogo -Command "Set-Location -LiteralPath '$PSScriptRoot'"

This is very helpful to me, thank you.

is there any way to the the same on MacOS?

open terminal and run:
open -a "Microsoft Edge" --args --disable-features=msFeatureGroupNewLookAndFeelHoldout

Now never totally close the opened edge app, you can close all its windows though, all new windows won't have the stupid rounded corners.
That's what Ive done.

Thank you so much!
Edge's rounded corners are such a fucking ugly UI. It was so disgusting.

Check out the new GUI tool, can optionally restore sidebar for anyone interested!

Is there a way to change the colour of the blue border ? or even disable i? thank you in advance Thorsten

Sorry, which blue border?