Comment # 1 on bug 1189205 from M. Edwin Zakaria

I can make it work after downgrading several python packages and installed it
using pip

python-flask==1.1.4
python-flask-security-too==3.3.3
python-psycopg2==2.8.6
python-wtforms==2.2.1

Need to set the python path after that in pgadmin4 configuration for
/usr/local/bin and /usr/local/lib/python3.8/site-packages.

Source https://bbs.archlinux.org/viewtopic.php?id=266423