Question about Lenovo IdeaPad Flex 5i

That is primarily also the question of your power bank. There are also some with 230 volt connection and how long you want to operate the device. There are certainly better suited because this device is not primarily designed for USB-C PD because it comes with a conventional power supply ;) Therefore, look for devices that have USB-C PD, then you will also see how many watts they accept for charging and you will know what kind of powerbank is the right one.