To all whom, gave input, thanks!
I finally found that the problem was hardware based. After changing config.txt by adding the line “dtoverlay gpio-shutdown,gpio_pin=3” the button did what it should do. After some reboots suddenly NOT any more. Be-course, I’d tried every other syntax, I’d determined that it had to be hardware related. Pure by chance I tried my 2 hand bought 3A power-supply, to use for charging my drained TomTom and it wouldn’t charge, or start.
Connected a different adapter, to the Pi and behold, after reboot I did got a shutdown menu. After renaming keyboard.xmlt back to keyboard.xml, the button performed a shutdown as it should time after time
There was another problem. To surch a switch; wires; connectors for GPIO in my things/stock, I found a suitable button and two pieces of wire with a connector, saved from a old desktop. For experimenting reasons, I didn’t shortened the wires, but soldered them to de two ends on de button.
Twisted the black and red wires and began experimenting. It made a cable approx 15cm and left it dangling of the RPi when the alterations took effect and the Pi was shutdown, after a few minutes it booted again, probably as a result of the to long wires working like antenna, or capacitator, when I rolled the cable together that problem was also solved.