EXT:jquery allows you to use jQuery in your extensions.
The extension version only matches the jQuery library version, it doesn't mean anything else.
You can load the library in your Fluid template.
<f:asset.script identifier="jquery" src="{jq:uri.js()}" />
Or use the slim version.
<f:asset.script identifier="jquery" src="{jq:uri.js(build: 'slim')}" />
To use other jQuery source, you can register it in ext_localconf.php or AdditionalConfiguration.php.
\Dagou\Jquery\Utility\ExtensionUtility::registerSource(\Dagou\Jquery\Source\StackPath::class);
You may want to disable the source and use the local one instead in some cases, for example saving page as PDF by WKHtmlToPdf.
{jq:uri.js(forceLocal: "true")}