diff --git i/src/Composer/Util/Http/CurlDownloader.php w/src/Composer/Util/Http/CurlDownloader.php
index 4f2fdb028..44e46d01d 100644
--- i/src/Composer/Util/Http/CurlDownloader.php
+++ w/src/Composer/Util/Http/CurlDownloader.php
@@ -242,7 +242,7 @@ private function initDownload(callable $resolve, callable $reject, string $origi
         if (0 === strpos($url, 'https://')) {
             $willUseProxy = $proxy->getStatus() !== '' && !$proxy->isExcludedByNoProxy();
 
-            if (!$willUseProxy && \defined('CURL_VERSION_HTTP3') && \defined('CURL_HTTP_VERSION_3') && (CURL_VERSION_HTTP3 & $features) !== 0) {
+            if (false) {
                 curl_setopt($curlHandle, CURLOPT_HTTP_VERSION, CURL_HTTP_VERSION_3);
             } elseif (\defined('CURL_VERSION_HTTP2') && \defined('CURL_HTTP_VERSION_2_0') && (CURL_VERSION_HTTP2 & $features) !== 0) {
                 curl_setopt($curlHandle, CURLOPT_HTTP_VERSION, CURL_HTTP_VERSION_2_0);