When running headless selenium in cron, got error "Pyperclip could not find a copy/paste mechanism for your system"

I have implemented a selenium script in Python to upload some pictures and content to Facebook, which I named FBUpload.py.

When I launch it this way, it works perfectly (in headless mode):

Xvfb :10 -ac &
python3 /home/someuser/scripts/FBUpload.py

Problem is, when I try to configure a cronjob that launches this same script, this way:

00 * * * * Xvfb :10 -ac &
01 * * * * python3 /home/someuser/scripts/FBUpload.py
45 * * * * kill -9 $(ps -auxw |grep Xvf|head -1| awk '{print $2}')

Then it fails with the following error:

Pyperclip could not find a copy/paste mechanism for your system

This is my setup: Ubuntu 20.04.4 LTS | Python3 | pyperclip 1.7.0

These are the Copy & paste mechanisms that I already installed:

PyQt5 5.15.6
PyQt5-Qt5 5.15.2
PyQt5-sip 12.10.1
QtPy 2.1.0
xclip 0.13-1 (in /usr/bin because it was installed via apt)
xsel 1.2.0+git9bfc13d.20180109-3 (in /usr/bin because it was installed via apt)

(I couldn't download PyQt4 or qkt as described in this post: pyperclip module raising an error message so I downloaded QtPy following the suggested solution. But the problem persists.)

I tried the fixes from posts with similar issue but none of them work for me. I am wondering if the issue has to do with users (because when I run the script with "sudo", the root user cannot find the libraries installed by the non-root user).

I also found this other question which seems to be similar (but instead of cron, the problem is systemd): Ubuntu 16.04 - Python 3 - Pyperclip in terminal and via systemd

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