Target connection fails with "Cannot identify target as a stm32x" (although STM32L053 works)
Okay, here's what I did:
In the meantime, I tried to replace the binarys of OpenOCD and the config files with each other, which lead everytime to a working setup outside of System Workbench.
(Of course, I reverted it all back).
So, the config files can't be the (only) cause for my problem.
I switched back to the original Nucleo ST-Link debugger (and edited the config file stm32f0_blinky.cfg entry back from interface/stlink-v2.cfg to interface/stlink-v2-1.cfg).
Still, the result is the same (sidenode: It's reproducable that the original ST-Link seems to be unable to read the target voltage successful, perhaps this is a hint? Measured the voltage on debugger-side again, so the connection is ok).
Also, I rechecked the VSSA (tied to GND) and VDDA (tied to 3.3 V) connections aaaand bingo:
(I'm a little bit embarressed to write it here as an electrical engineer)
I had a cold soldering point at the VDDA connection.
Somehow, now I'm able to establish a stable debug session with the original ST-Link and the cloned one, as well.
I still don't get and am really interested in the answer, why a missing power supply for the ADC can lead to a flashable board using the ST-Link Utility, but not with the System Workbench toolchain?
To be honest I don't trust the board an inch at the moment and will play with it around a little bit more, but it seems it's now working 😊
Thanks a lot for the moment to everyone who wrote here and tried to help, especially LaurentL! 😀