As flask-script is no longer maintaned and no longer compatible with flask:
$ python manage.py
Traceback (most recent call last):
File "/home/mdk/clones/Flask-AdminLTE3/sample_application/manage.py", line 4, in <module>
from flask_script import Manager
File "/home/mdk/clones/Flask-AdminLTE3/.venv/lib/python3.9/site-packages/flask_script/__init__.py", line 15, in <module>
from flask._compat import text_type
ModuleNotFoundError: No module named 'flask._compat'
As flask-script is no longer maintaned and no longer compatible with flask: