I haven't seen this error before, I also don't use Django so possibly this is why. A quick google shows a lot of people suggesting to try and install the libffi-devel package (if you're working on linux?)

It might be an issue between Django and 3.9 too which will need time to be fixed. If there are no clear fixes, I would ask on stackoverflow and if no-one is able to help revert back to 3.8 for a while

Sorry I couldn't help more!