Yes, I got it.
I have the bare metal blinking sample fro Simplicity studio runing at less than 10µA!
It’s just… as simple as disabling SWD pins:
GPIO->DBGROUTEPEN = 0;
Update:
To be more precise, the register is described in the erf32mg24 reference manual page 903. It is GPIO_DBGROUTEPEN bits SWDIOTMSPEN and SWCLKTCKPEN.
The solution also works on the Zigbee Device.