While making the new WT look and feel like Powershell, the selectionBackground property seems affected by an acrylic effect that reduces contrast for accessibility and causes an ugly sensation whit some color schemes. It should be a true/false option that triggers the cmd/powershell mode (full opacity). In that case, a selectionForeground could be added too, in order to address the parity features with conhost.exe.

A technical implementation in profiles.json could be something like this (don´t have enough C++ knowledge for real code):

"profiles":
    {
        "list":
        [
            {
                "name": "Windows PowerShell",
                "commandline": "powershell.exe",
                "selectionOpacity": true,
                "selectionBackground": "#fedba9",
                "selectionForeground": "#ffffff",
                "hidden": false
             }
        ]
    }