PHP GD and WebP support:

Normal WebP (VP8): supported since PHP 5.4
Transparent WebP or alpha transparency (VP8X, VP8L): supported since PHP 7.0
Animated WebP (VP8X): not supported at all.

You can use the images from here https://developers.google.com/speed/webp/gallery2
here https://ezgif.com/help/alternative-animated-image-formats
and here https://developers.google.com/speed/webp/gallery1

Test with imagecreatefromwebp('your-image.webp'); and see the errors.

You can detect animated or transparent webp using this code.

<?php
/**
 * Get WebP file info.
 * 
 * @link https://www.php.net/manual/en/function.pack.php unpack format reference.
 * @link https://developers.google.com/speed/webp/docs/riff_container WebP document.
 * @param string $file
 * @return array|false Return associative array if success, return `false` for otherwise.
 */
function webpinfo($file) {
    if (!is_file($file)) {
        return false;
    } else {
        $file = realpath($file);
    }

    $fp = fopen($file, 'rb');
    if (!$fp) {
        return false;
    }

    $data = fread($fp, 90);

    fclose($fp);
    unset($fp);

    $header_format = 'A4Riff/' . // get n string
        'I1Filesize/' . // get integer (file size but not actual size)
        'A4Webp/' . // get n string
        'A4Vp/' . // get n string
        'A74Chunk';
    $header = unpack($header_format, $data);
    unset($data, $header_format);

    if (!isset($header['Riff']) || strtoupper($header['Riff']) !== 'RIFF') {
        return false;
    }
    if (!isset($header['Webp']) || strtoupper($header['Webp']) !== 'WEBP') {
        return false;
    }
    if (!isset($header['Vp']) || strpos(strtoupper($header['Vp']), 'VP8') === false) {
        return false;
    }

    if (
        strpos(strtoupper($header['Chunk']), 'ANIM') !== false || 
        strpos(strtoupper($header['Chunk']), 'ANMF') !== false
    ) {
        $header['Animation'] = true;
    } else {
        $header['Animation'] = false;
    }

    if (strpos(strtoupper($header['Chunk']), 'ALPH') !== false) {
        $header['Alpha'] = true;
    } else {
        if (strpos(strtoupper($header['Vp']), 'VP8L') !== false) {
            // if it is VP8L, I assume that this image will be transparency
            // as described in https://developers.google.com/speed/webp/docs/riff_container#simple_file_format_lossless
            $header['Alpha'] = true;
        } else {
            $header['Alpha'] = false;
        }
    }

    unset($header['Chunk']);
    return $header;
}// webpinfo
?>

Reference: https://stackoverflow.com/a/68491679/128761

Usage:

<?php
$info = webpinfo('your-image.webp');
if (isset($info['Animation']) && $info['Animation'] === true) {
    echo 'It is animated webp.';
} 
if (isset($info['Alpha']) && $info['Alpha'] === true) {
    echo 'It is transparent webp.';
} 
?>