Unable to start screen session using Run From source documentation

Hello,
I am new with the tool and tried to follow the documentation Run From Sources — StackStorm 3.3.0 documentation because I am using ubuntu 20.10, so far found some packages that seems to need an update and I am willing to create a PR to update the documentation, but at the moment I am stuck with an error:
ERROR: Unable to start screen session for st2-rulesengine.
ERROR: Unable to start screen session for st2-timersengine.
ERROR: Unable to start screen session for st2-garbagecollector.

When I execute:
./tools/launchdev.sh start

On logs/screen-st2rulesengine.log found:
Traceback (most recent call last):
File “./st2reactor/bin/st2rulesengine”, line 23, in
from st2reactor.cmd import rulesengine
ModuleNotFoundError: No module named ‘st2reactor’

Same on /logs/screen-st2-timersengine.log:
Traceback (most recent call last):
File “./st2reactor/bin/st2timersengine”, line 23, in
from st2reactor.cmd import timersengine
ModuleNotFoundError: No module named ‘st2reactor’

Any guidance on what should I do next is appreciated.

The issue you’re most likely having because Ubuntu 20.x has python 3.8 available, while StackStorm currently supports python 3.6 only.

There are plans to add Ubuntu 20 and python 3.8 support in the future StackStorm versions (see Ubuntu 20.04 LTS Support · Issue #4920 · StackStorm/st2 · GitHub).

Before that happens, please use one of the supported OS platforms: Ubuntu 16.04/18.04 LTS or RHEL/CentOS 7/8 for running or developing StackStorm.
Hope that helps.