The main one everybody uses at least from my knowledge and from what I've used over the last 13 years is UFW. That is what you want to use.

A firewall is very important not just for being on public Wi-Fi connections. A firewall is your extra layer of protection

I don't know what Distro you run. But it's almost the same for each one

https://www.digitalocean.com/community/tutorials/how-to-set-up-a-firewall-with-ufw-on-ubuntu-20-04

UFW is installed by default on Ubuntu. If it has been uninstalled for some reason, you can install it with sudo apt install ufw.

Using IPv6

sudo nano /etc/default/ufw

That command should come back with this

IPV6=yes

Save and close the file. Now, when UFW is enabled, it will be configured to write both IPv4 and IPv6 firewall rules. However, before enabling UFW, we will want to ensure that your firewall is configured to allow you to connect via SSH. Let’s start with setting the default policies.

Setting up default policies

sudo ufw default deny incoming sudo ufw default allow outgoing

These commands set the defaults to deny incoming and allow outgoing connections. These firewall defaults alone might suffice for a personal computer, but servers typically need to respond to incoming requests from outside users. We’ll look into that next.

To configure your server to allow incoming SSH connections, you can use this command:

sudo ufw allow ssh

This will create firewall rules that will allow all connections on port 22, which is the port that the SSH daemon listens on by default. UFW knows what port allow ssh means because it’s listed as a service in the /etc/services file.

However, we can actually write the equivalent rule by specifying the port instead of the service name. For example, this command works the same as the one above:

sudo ufw allow 22

If you configured your SSH daemon to use a different port, you will have to specify the appropriate port. For example, if your SSH server is listening on port 2222, you can use this command to allow connections on that port:

sudo ufw allow 2222

To enable UFW, use this command:

sudo ufw enable

I see that both UFW and firewalld are recommended... is it basically OK whichever I choose?

Yes. Whichever works for you should be fine. In the end you should be able to manage it