To trim image using Imagick() with 20% fuzziness use

$image->trimImage(0.20 * $image::getQuantum());

or

$image->trimImage(0.20 * Imagick::getQuantum());

https://phpimagick.com/Imagick/trimImage

And in case of Gmagick()

$max_quantum = 65535;
switch ($image->getQuantumDepth()['quantumDepthLong']) {
    case  8: $max_quantum = 255; break;
    case 16: $max_quantum = 65535; break;
    case 32: $max_quantum = 4294967295; break;
}
$image->trimImage(0.20 * $max_quantum);