Jetpack uselessly enqueues Thickbox JS (which itself enqueues jQuery!) when rendering the Subscriptions block, even though it doesn't even use Thickbox. I use this snippet on my own site to fix it.

prevent-jetpack-subscriptions-thickbox.php

<?php

/**
 * Fix Jetpack Subscriptions block to not uselessly enqueue Thickbox, which in turn enqueues jQuery.
 */
function felixarntz_stop_jetpack_subscriptions_from_enqueuing_thickbox_without_any_usage() {
	if ( wp_script_is( 'jetpack-block-subscriptions' ) && isset( wp_scripts()->registered['jetpack-block-subscriptions'] ) ) {
		$script = wp_scripts()->registered['jetpack-block-subscriptions'];
		$index  = array_search( 'thickbox', $script->deps, true );
		if ( false !== $index ) {
			unset( $script->deps[ $index ] );
			$script->deps = array_values( $script->deps );
		}

		// Also add 'defer' since this script does not need to be _immediately_ loaded.
		$script->add_data( 'strategy', 'defer' );

		// This here is needed since sometimes that script is generally enqueued as well.
		// Probably not needed?
		if ( wp_script_is( 'thickbox' ) ) {
			wp_dequeue_script( 'thickbox' );
		}
	}
}
add_action( 'wp_enqueue_scripts', 'felixarntz_stop_jetpack_subscriptions_from_enqueuing_thickbox_without_any_usage' );
add_action( 'wp_footer', 'felixarntz_stop_jetpack_subscriptions_from_enqueuing_thickbox_without_any_usage' );