OneButton with pins A6 and A7 I noticed that OneButton library does not work with pins A6 and A7 (with A1 and A2 it works good) on my Arduino Nano. Is it because A6 and A7 are Analog only? There is possibility to make them work properly?

sketch example is here https://github.com/mathertel/OneButton/blob/master/examples/TwoButtons/TwoButtons.ino
Pins A6 and A7 are analog only pins. They have no digital functionality at all. 



You can see that pins 19 and 22 only have ADCn on them - no Pxn for digital operation (ignore the colour scheme of those pins - that's an error in the datasheet).