matej@pmd85:~$ python -m venv testqt
matej@pmd85:~$ source testqt/bin/activate
(testqt) matej@pmd85:~$ which python

/home/matej/testqt/bin/python

(testqt) matej@pmd85:~$ python --version

Python 3.9.0

(testqt) matej@pmd85:~$ pip install pyside2

Looking in links: /home/matej/.pip/wheels
Collecting pyside2
  Using cached PySide2-5.15.2-5.15.2-cp35.cp36.cp37.cp38.cp39-abi3-manylinux1_x86_64.whl (164.3 MB)
Collecting shiboken2==5.15.2
  Using cached shiboken2-5.15.2-5.15.2-cp35.cp36.cp37.cp38.cp39-abi3-manylinux1_x86_64.whl (956 kB)
Installing collected packages: shiboken2, pyside2
Successfully installed pyside2-5.15.2 shiboken2-5.15.2
WARNING: You are using pip version 20.2.2; however, version 20.2.4 is available.
You should consider upgrading via the '/home/matej/testqt/bin/python -m pip install --upgrade pip' command.

(testqt) matej@pmd85:~$ python -c 'from PySide2 import QtCore'

(testqt) matej@pmd85:~$