A little powershell script that sets the default microphone volume to a set value, requires nircmd.exe to be in same directory as the script

lockmicvolume.ps1

# How long it should wait between every loop in seconds
$secondsToWait = 5
# The volume you want in percent (0.92 = 92%)
$volume = 1.00

Write-Host "Starting invinite loop, press CTRL + C or close the window to stop"
while (1) {
  Start-Process -FilePath "nircmd.exe" -WorkingDirectory $PSScriptRoot -ArgumentList "setsysvolume $([math]::floor(65535 * $volume))","default_record" -Wait
  Write-Host "Volume set to $($volume * 100)%"
  Start-Sleep -Seconds $secondsToWait
}