@StephPTi Well, I did not use Android extensively, only for some minor looking around (it is awful 😊 ), but I did not notice anything wrong with the button or the system...
The device came with Android 11, I downgraded to Android 10 using the image:
surya_global_images_V12.0.9.0.QJGMIXM_20210508.0000.00_10.0_global
...and using the attached script 'flash_all.sh'.
I'm thinking if there is a way to re-image it back to Android now? To check, if the button worked ok? (I never re-imaged UBports phone back to Android before, so not sure about the implications...)