I had a similar error (not completely the same) after installing orjson library.
It worked after deleting the library in my venv.
Hope it helps.
Thanks for reporting @Gordon_Shapiro ! Any chance you can share the error message and a minimum reproducible example? Would be really helpful. I believe that the error that you encountered with orsjon would be different than the error reported in Dash 2.0.0 migration error - #3