Comment 8 for bug 1837143

Isn't it "just" a missing package?
on a rhel8 with osp-15/Stein, python3:
[stack@undercloud ~]$ /usr/libexec/platform-python -s
Python 3.6.8 (default, Apr 3 2019, 17:26:03)
[GCC 8.2.1 20180905 (Red Hat 8.2.1-3)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from jinja2 import Template
>>>
[stack@undercloud ~]$ rpm -qa | grep jinja2
python3-jinja2-2.10.1-2.el8_0.noarch
[stack@undercloud ~]$ rpm -qa | grep markupsafe
python3-markupsafe-1.1.0-2.el8ost.x86_64
[stack@undercloud ~]$

Care to check/ensure you have that python3-markupsafe thingy?