I installed firewall-configuration and lost the wifi

to keep the PC safe, I installed firewall-configuration from Ubuntu software:

As soon as the installation was over, I lost the WiFi connection (and even Rstudio cannot connect with R, by the way). I removed it with sudo apt-get remove firewall-config but the WiFi is still dead.

How can I reestablish the wifi? and do I need a firewall in ubuntu? and an antivirus? (if yes, is clamAV OK?)

Thanks

You may have removed the firewall-config software, but the firewall rules may still be applying to your connections. Try to clear them with these commands:

sudo iptables -P INPUT ACCEPT
sudo iptables -P OUTPUT ACCEPT
sudo iptables -P FORWARD ACCEPT
sudo iptables -F

Then maybe reboot to make sure they've been cleared.

Another thing you can try is to disable the Uncomplicated Firewall ufw used by Ubuntu:

sudo ufw disable

If you want to use a firewall in Ubuntu, I recommend you read about how to use ufw.