According to docu here, nano 33 BLE should support debugging, as the text in the link says: As of today, the debugger supports all the Arduino boards based on the SAMD and Mbed platforms (MKR family, Nano 33 IoT, Nano 33 BLE, Portenta, Zero).).
Hi @xrk. Unfortunately this is not really supported right now. The only boards that have true support are the SAMD boards (e.g., Zero, MKR, Nano 33 IoT). It is theoretically possible to use the debugger with the Nano 33 BLE, but there is currently no documentation for how to do this and it is not a point and click operation like it is with the SAMD boards.
If you study the information provided at the links I shared here and do enough experimentation, you will probably be able to achieve it:
Trying to debug, I am asked for a configuration in form of a launch.json file (screenshot attached). What should I enter here? I see in some websites that the configuration for some includes also "Arduino" - I only have "No Configurations / Add Configuration" ?
If the platform was configured for full debugger support, as it is for the SAMD boards, then that would be the case. You could just click the debug button and it would be all configured for use with any CMSIS-DAP compliant debug probe.
In the case of boards platforms that are not configured, or other types of debug probes, it is necessary to do the configuration yourself. There is some information about that off of the link I shared above.
Also for my understanding - do I need additional debugger soldered onto the 5 pins on the bottom of the PCB, such as ST/Link or Segger J-Link, for the debugging to work on nano 33 BLE Sense, or does it work via std. USB connection?
You do need a hardware debug probe. I don't know whether you would be able to use the ST-Link with the Nano 33 BLE. I have done some research on that subject and it seemed like it is maybe possible with some custom firmware, but not guaranteed.
The J-Link is definitely usable. In fact, Segger even provides some documentation specifically for the Nano 33 BLE, though not specific to Arduino IDE 2.x:
This requirement for a separate debug probe is the case for most of the Arduino boards. The Zero is an exception because it has a built-in CMSIS-DAP compliant debug probe, so that is a very convenient board to use with the Arduino IDE 2.x debugger.
The Arduino Portenta H7 also has the ability for debugging without any extra hardware, but this is done using the Lauterbach TRACE32 debugger application rather than the Arduino IDE 2.x: