Tax Calculation

Yes, this is definitely achievable with some custom code. You can implement the attached code by adding it to your active theme’s functions.php file.

/**
 * Use TeraWallet's taxable-fee branch, which lets WooCommerce apportion the
 * negative fee's tax across the cart's tax classes instead of stripping it.
 */
add_filter( 'woo_wallet_partial_payment_tax_mode', static function () {
	return 'tax_inclusive_wallet';
}, 99 );

/**
 * Stop that branch grossing the fee base down by the tax rate. With rate 0 the
 * fee base is the entered wallet amount, so WooCommerce's negative fee tax
 * shrinks the taxable base by exactly that amount. Also caps the applied amount
 * at the cart's ex-tax total, which is WooCommerce's own negative-fee ceiling.
 */
add_filter( 'woo_wallet_partial_payment_effective_tax_rate', '__return_zero', 99 );

/**
 * Debit only the fee base, not base + its negative tax.
 *
 * Core's get_order_partial_payment_amount() returns abs( total + total_tax ),
 * which here would over-debit by the tax the wallet is not paying.
 *
 * @param float $amount   Amount core derived.
 * @param int   $order_id Order ID.
 * @return float
 */
add_filter( 'woo_wallet_order_partial_payment_amount', static function ( $amount, $order_id ) {
	if ( ! function_exists( 'is_partial_payment_order_item' ) ) {
		return $amount;
	}

	$order = wc_get_order( $order_id );
	if ( ! $order ) {
		return $amount;
	}

	$total = 0.0;
	foreach ( $order->get_items( 'fee' ) as $item_id => $item ) {
		if ( is_partial_payment_order_item( $item_id, $item ) ) {
			$total += (float) $item->get_total( 'edit' );
		}
	}

	return abs( $total );
}, 99, 2 );