Getting the following:

Error: class uri 'gevent' invalid or not found:

[Traceback (most recent call last):
File "/usr/local/lib/python3.8/site-packages/gunicorn/workers/ggevent.py", line 13, in <module>
import gevent
ModuleNotFoundError: No module named 'gevent'

During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "/usr/local/lib/python3.8/site-packages/gunicorn/util.py", line 99, in load_class
mod = importlib.import_module('.'.join(components))
File "/usr/local/lib/python3.8/importlib/__init__.py", line 127, in import_module
return _bootstrap._gcd_import(name[level:], package, level)
File "<frozen importlib._bootstrap>", line 1014, in _gcd_import
File "<frozen importlib._bootstrap>", line 991, in _find_and_load
File "<frozen importlib._bootstrap>", line 975, in _find_and_load_unlocked
File "<frozen importlib._bootstrap>", line 671, in _load_unlocked
File "<frozen importlib._bootstrap_external>", line 843, in exec_module
File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
File "/usr/local/lib/python3.8/site-packages/gunicorn/workers/ggevent.py", line 15, in <module>
raise RuntimeError("gevent worker requires gevent 1.4 or higher")
RuntimeError: gevent worker requires gevent 1.4 or higher
]

Changed Dockerfile to:

FROM python:3.8
RUN apt update
RUN pip3 install flask
RUN pip3 install gevent
RUN pip3 install gunicorn
RUN pip3 install gunicorn
COPY ./main.py /home/main.py
WORKDIR /home
CMD gunicorn --keep-alive 10 -k gevent --bind 0.0.0.0:5000 -w 20 main:app

Works now