load-mu-plugins-from-dirs.php

<?php
$flags = \FilesystemIterator::KEY_AS_PATHNAME | \FilesystemIterator::SKIP_DOTS;
$iterator = new \FilesystemIterator(__DIR__, $flags);

foreach ($iterator as $path => $item) {
    if ($item->isDir()) {
        $muPath = trailingslashit($path);
        $fileName = basename($item->getFileName());
        $filePath = "{$muPath}/{$fileName}.php";

        if (file_exists($filePath)) {
            require_once $filePath;
        }
    }
}

Save this code in a file and place it in WordPress mu-plugins folder. It will load all mu-plugins that are inside directories. But, the entry file must match the plugin directory name. Example:

my-nice-plugin/my-nice-plugin.php