I’m having a similar error. I think there are some breaking changes when updating from python2 to python3.
This is perfectly fine with python2 but broke with python3
So I came up with a patch:
https://github.com/nguyennk92/edx-platform/commit/e70cf63180b3acd5e19032235595c880cb35bc20.patch
It basically just encode the transcript content before passing to ContentFile
Apply it to Dockerfile and rebuild image:
RUN curl https://github.com/nguyennk92/edx-platform/commit/e70cf63180b3acd5e19032235595c880cb35bc20.patch | git apply -