thanks @hfollmann for the info regarding the firewalld installation, that means the GUI for that should be firewall-config which can be installed with
sudo apt install firewall-config but firewalld should be able to tell you if it’s running with the comand
sudo firewall-cmd --state and with
sudo firewall-cmd --list-all it should tell you it’s configuration.
With those commands you should be able to figure out if it’s running or not and how it’s configured.
this can also be done with the
firewall-config if you want to install it.
But I’d also repeat @Kyle_Rankin advice to install OpenSnitch even though that can be quite confusing for new users since a wrong click can more or less disconnect you from the net at least it’s gonna look like that, best advice to keep that from happening is to initial set all OpenSnitch configs to next reboot that you everything setting is gone after a reboot.
And please be aware that most of the hardening guidelines for Linux on the web are for remote controlled Server not end user devices.