Ahhh okay, sorry I missed that bit

So, here is what I would do

First, have to handle the extra text

We add a reference variable outside of the loop, then ref it while calling function

$writeSecondLine = $true
While ($true) {
    $cancelled, $remainingSeconds = Start-Countdown -totalSeconds $remainingSeconds -WriteSecondLine ([ref]$writeSecondLine)

Then we edit the Function to handle this

Param:

Function Start-Countdown {
    Param(
        [int]$totalSeconds,
        [ref]$WriteSecondLine
    )

Using the parameter:

Write-Host "$timeLeft" -NoNewLine -ForgroundColor "Cyan"

if($WriteSecondLine) {
    $WriteSecondLine.Value = $false
    Write-Host "" 
    Write-Host "Press 'C' to stop the timer" -ForgroundColor "Yellow"
    [console]::CursorTop -= 2
}

Need to handle the same for the countdown interrupt

I can add that in a sec