ERROR: Could not find a version that satisfies the requirement rasa==2.8.21 (from -r requirements.txt (line 1))

[hack-r]

Python 3.9 in a fresh venv:

% source myEnv/bin/activate
% make install
python -m pip install --upgrade "pip<20"
Collecting pip<20
  Downloading pip-19.3.1-py2.py3-none-any.whl (1.4 MB)
     |████████████████████████████████| 1.4 MB 344 kB/s 
Installing collected packages: pip
  Attempting uninstall: pip
    Found existing installation: pip 21.2.4
    Uninstalling pip-21.2.4:
      Successfully uninstalled pip-21.2.4
Successfully installed pip-19.3.1
pip install -r requirements.txt
ERROR: Could not find a version that satisfies the requirement rasa==2.8.21 (from -r requirements.txt (line 1)) (from versions: 0.0.1, 0.0.2, 0.0.3, 0.0.4, 0.0.5, 0.1.0, 0.1.1, 0.2.0a2, 0.2.0a3, 0.14.0a5, 0.14.0a6, 0.14.0a7, 0.14.0a8, 0.14.0a9, 0.15.0a6, 1.0.0a1, 1.0.0a2, 1.0.0a3, 1.0.0a4, 1.0.0a5, 1.0.0rc1, 1.0.0rc2, 1.0.0rc3, 1.0.0rc4, 1.0.0rc5, 1.0.0rc6, 1.0.0rc7, 1.0.0rc8, 1.0.0rc9, 1.0.0rc10, 1.0.0rc11, 1.0.0rc12, 1.0.0, 1.0.1, 1.0.2, 1.0.3, 1.0.4, 1.0.5, 1.0.6, 1.0.7, 1.0.8, 1.0.9, 1.1.0, 1.1.1, 1.1.2, 1.1.3, 1.1.4, 1.1.5, 1.1.6, 1.1.7, 1.1.8, 1.2.0a2, 1.2.0a3, 1.2.0a4, 1.2.0a5, 1.2.0a6, 1.2.0a7, 1.2.0, 1.2.1, 1.2.2, 1.2.3, 1.2.4, 1.2.5, 1.2.6, 1.2.7, 1.2.8, 1.2.9, 1.2.10, 1.2.11, 1.2.12, 1.3.0a1, 1.3.0a2, 1.3.0, 1.3.1a1, 1.3.1a3, 1.3.1a4, 1.3.1a5, 1.3.1a8, 1.3.1a10, 1.3.1a11, 1.3.1a12, 1.3.1a14, 1.3.1, 1.3.2, 1.3.3, 1.3.4, 1.3.6, 1.3.7, 1.3.8, 1.3.9, 1.3.10, 1.4.0, 1.4.1, 1.4.2, 1.4.3, 1.4.4, 1.4.5, 1.4.6, 1.5.0, 1.5.1, 1.5.2, 1.5.3, 1.6.0a1, 1.6.0a2, 1.6.0, 1.6.1, 1.6.2, 1.7.0, 1.7.1, 1.7.2, 1.7.3, 1.7.4, 1.8.0, 1.8.1, 1.8.2, 1.8.3, 1.9.0, 1.9.1, 1.9.2, 1.9.3, 1.9.4, 1.9.5, 1.9.6, 1.9.7, 1.10.0a1, 1.10.0a2, 1.10.0, 1.10.1, 1.10.2, 3.1.0, 3.1.1, 3.1.2, 3.1.3, 3.1.4, 3.1.5, 3.1.6, 3.1.7, 3.2.0, 3.2.1, 3.2.2, 3.2.4, 3.2.5, 3.2.6, 3.2.7, 3.2.8, 3.2.10, 3.2.11, 3.2.12, 3.2.13, 3.3.0a1, 3.3.0, 3.3.1, 3.3.2, 3.3.3, 3.3.4, 3.3.5, 3.3.6, 3.3.7, 3.3.8, 3.3.9, 3.3.10, 3.3.11, 3.4.0, 3.4.1, 3.4.2, 3.4.3, 3.4.4, 3.4.5, 3.4.6, 3.4.7, 3.4.8, 3.4.9, 3.4.10, 3.4.11, 3.4.12, 3.4.13, 3.5.0a1.dev1, 3.5.0a2.dev1, 3.5.0a2.dev2, 3.5.0b1, 3.5.0, 3.5.1, 3.5.2, 3.5.3, 3.5.4, 3.5.5, 3.5.6, 3.5.7, 3.5.8, 3.5.9, 3.5.10, 3.6.0a1)
ERROR: No matching distribution found for rasa==2.8.21 (from -r requirements.txt (line 1))
WARNING: You are using pip version 19.3.1; 

Furthermore:

% git checkout 3.0_upgrade 
branch '3.0_upgrade' set up to track 'origin/3.0_upgrade'.
Switched to a new branch '3.0_upgrade'
(myEnv) % make install
python -m pip install --upgrade "pip<20"
Requirement already up-to-date: pip<20 in ./myEnv/lib/python3.9/site-packages (19.3.1)
WARNING: You are using pip version 19.3.1; however, version 23.1.2 is available.
You should consider upgrading via the 'pip install --upgrade pip' command.
pip install -r requirements.txt
ERROR: Could not find a version that satisfies the requirement rasa==3.0.8 (from -r requirements.txt (line 1)) (from versions: 0.0.1, 0.0.2, 0.0.3, 0.0.4, 0.0.5, 0.1.0, 0.1.1, 0.2.0a2, 0.2.0a3, 0.14.0a5, 0.14.0a6, 0.14.0a7, 0.14.0a8, 0.14.0a9, 0.15.0a6, 1.0.0a1, 1.0.0a2, 1.0.0a3, 1.0.0a4, 1.0.0a5, 1.0.0rc1, 1.0.0rc2, 1.0.0rc3, 1.0.0rc4, 1.0.0rc5, 1.0.0rc6, 1.0.0rc7, 1.0.0rc8, 1.0.0rc9, 1.0.0rc10, 1.0.0rc11, 1.0.0rc12, 1.0.0, 1.0.1, 1.0.2, 1.0.3, 1.0.4, 1.0.5, 1.0.6, 1.0.7, 1.0.8, 1.0.9, 1.1.0, 1.1.1, 1.1.2, 1.1.3, 1.1.4, 1.1.5, 1.1.6, 1.1.7, 1.1.8, 1.2.0a2, 1.2.0a3, 1.2.0a4, 1.2.0a5, 1.2.0a6, 1.2.0a7, 1.2.0, 1.2.1, 1.2.2, 1.2.3, 1.2.4, 1.2.5, 1.2.6, 1.2.7, 1.2.8, 1.2.9, 1.2.10, 1.2.11, 1.2.12, 1.3.0a1, 1.3.0a2, 1.3.0, 1.3.1a1, 1.3.1a3, 1.3.1a4, 1.3.1a5, 1.3.1a8, 1.3.1a10, 1.3.1a11, 1.3.1a12, 1.3.1a14, 1.3.1, 1.3.2, 1.3.3, 1.3.4, 1.3.6, 1.3.7, 1.3.8, 1.3.9, 1.3.10, 1.4.0, 1.4.1, 1.4.2, 1.4.3, 1.4.4, 1.4.5, 1.4.6, 1.5.0, 1.5.1, 1.5.2, 1.5.3, 1.6.0a1, 1.6.0a2, 1.6.0, 1.6.1, 1.6.2, 1.7.0, 1.7.1, 1.7.2, 1.7.3, 1.7.4, 1.8.0, 1.8.1, 1.8.2, 1.8.3, 1.9.0, 1.9.1, 1.9.2, 1.9.3, 1.9.4, 1.9.5, 1.9.6, 1.9.7, 1.10.0a1, 1.10.0a2, 1.10.0, 1.10.1, 1.10.2, 3.1.0, 3.1.1, 3.1.2, 3.1.3, 3.1.4, 3.1.5, 3.1.6, 3.1.7, 3.2.0, 3.2.1, 3.2.2, 3.2.4, 3.2.5, 3.2.6, 3.2.7, 3.2.8, 3.2.10, 3.2.11, 3.2.12, 3.2.13, 3.3.0a1, 3.3.0, 3.3.1, 3.3.2, 3.3.3, 3.3.4, 3.3.5, 3.3.6, 3.3.7, 3.3.8, 3.3.9, 3.3.10, 3.3.11, 3.4.0, 3.4.1, 3.4.2, 3.4.3, 3.4.4, 3.4.5, 3.4.6, 3.4.7, 3.4.8, 3.4.9, 3.4.10, 3.4.11, 3.4.12, 3.4.13, 3.5.0a1.dev1, 3.5.0a2.dev1, 3.5.0a2.dev2, 3.5.0b1, 3.5.0, 3.5.1, 3.5.2, 3.5.3, 3.5.4, 3.5.5, 3.5.6, 3.5.7, 3.5.8, 3.5.9, 3.5.10, 3.6.0a1)
ERROR: No matching distribution found for rasa==3.0.8 (from -r requirements.txt (line 1))

Does it need a specific version of Python other than 3.9, or something?