I tried it once with my iPad Pro 10.5" (2017) and the Lightning to USB adapter and it works. This implies that it should also work on the iPad 6th Gen. The mouse I tested was the Dell USB UVDEL1. It may also be that a different mouse requires more power and therefore still needs to power the Lightning connector on the adapter. In any case, many storage media such as SSDs or USB sticks cannot be used without a power connection. This is not the case with the USB-C, i.e. iPad Pro (2018 or 2020), where the iPad has enough power with the connector so that all storage media and such can be plugged in. The Lightning connector simply doesn't bring enough power to the devices.
In any case, it is much more convenient to find a wireless mouse.
For those who don't know, all you have to do to use a mouse on the iPad is update the device to iOS version 13.4.
But the way to find the settings for the mouse buttons is still too complicated.