Trying not to fry another Nano

[PaulRB]

@abbesnabb

The leds does not need to be connected to power through the Arduino as I understand it now?

The LEDs must not be powered by or through the Arduino, it cannot withstand such high currents.

@abbesnabb

no connection to Arduino power

The Arduino needs power. Power it from the same buck converter to it's 5V pin. Do not connect it's Vin pin.

@abbesnabb

Get a proper original Arduino this time.

A proper original Arduino would have burned out exactly as the clone did.

@abbesnabb

Perhaps I could try to limit the power consumption as pointed out I am potentially underpowered if I run all the leds at maximum white.

I asked before what the maximum current of your buck converter is. If that can supply 7.5A then you should have no problem.

@abbesnabb

Is there a way to physically limit the maximum output (Ampere) or should I do that in the software, I could limit the maximum dim level.

If you use the FastLED library, it has that automatic limiting function built in to the library. You just have to set the max current with a function.