Remove specified shipping method(s) during free tier

add_filter( 'woocommerce_package_rates', function( $rates_orig ) {

	// Get Applicable Free Rate Object(s)
	$rates_free = [];
	foreach( $rates_orig as $rate_id => $rate ) {
		if( 'free_shipping' === $rate->method_id ) {
			$rates_free[ $rate_id ] = $rate;
			break;
		}
	}

	// Remove Equavalent Non Free Rate
	$rates_cleaned = [];
	foreach( $rates_orig as $rate_id => $rate ) {
		switch( $rate->label ) {

			// Match Our Free Tier Equivalent
			case 'Ground shipping (2 -7 business days)':
				break;

			// Keep Others
			default:
				$rates_cleaned[ $rate_id ] = $rate;
		}
	}

	// Return Cleaned Rate Objects When Free Shipping Is Available
	return empty( $rates_free ) ? $rates_orig : $rates_cleaned;

} );