some additional info:
" import tflite_runtime" does not trigger an error
" import tflite_runtime.interpreter" does trigger the same error as reported in the original post above
so, with some further research. it looks to be an error related to namespaces (but I am not an expert in how to use the import statements)
Could it be because I installed opencv separately before running the tensorflow lite installation instructions (which also seems to install opencv in the setup.sh shell script)?
I’ll start from scratch (again, already spent 3 days …)  but I hope someone can shed some light on this issue.