This script work 100% with clean Debian 11 box
First make sure to update and upgrade
sudo apt update && sudo apt -y full-upgrade && reboot
wget https://github.com/waelisa/Pritunl-VPN-on-Debian/raw/main/install-pritunl.sh
chmod u+x install-pritunl.sh
./install-pritunl.sh
Pritunl VPN server is now installed and running http://<your_server_ip>