someone else had this same error and solved it with different Ansible/python versions: Issues installing Ansible on Mac OS
I also found https://github.com/ansible/ansible/issues/64745 though it implied it was an issue with 2.9 and fixed in 2.9.1 (you were using 2.8.13)
The easiest thing I can think to try is forcing a newer version of Ansible. You can edit trellis/requirements.txt to look like this:
ansible>=2.9.1,<3.0
passlib
And run trellis exec pip install -r requirements.txt --upgrade. Running trellis exec ansible --version should show 2.9.1 at least I hope. Then try trellis up again please.