Was not my best weekend it seems - a lot of stupid careless mistakes…
I used the SerialFlash library and sent the device to sleep. After re-booting you have to call wakeup, even if SerialFlash.begin(FLASH_CS) fails.
The positove message: removing the LED, sending flash, LORA and CPU to deepsleep I achieved a power consumption of ~0.07mA measured on the LiPo battery…