In the meantime - with having much fun while debugging the debugger 
- I think I’ve found the origin of the strange python error. It’s the missing support for python 2.7 on my system.
piodebuggdb spawns to the real debugger - in my case xtensa-esp32s3-elf-gdb - which is dynamically linked to libpython2.7.so.1.0. Unfortunately this python version is not supported in my distribution (openSUSE 15.6). To circumvent the inevitable linkage error I had manually installed libpython2.7.so.1.0 a time ago to solve another problem with this missing lib.
Now I must hope that this already known issue is fixed soon 