[Post-Install] My system is built for fast clean installs. So I installed this great build.

[MichaelEber]

I tried doing the update, I even had the window coming up on my destop. But whenever I clicked on it I got and empty screen and an Error on attempting to access it.
So I downloaded the ISO and installed it clean. I then added Flatpak (don't know why this isn't installed!!!) after which I then installed ProtonPlus. This quickly gives me Proton-GE for Steam.
Finally I installed Steam, started the Firewall, and followed all 6 steps for "After you install Kubuntu" tasks. (Interestingly they don't say you have to activate a Firewall!)

While the performance of the system isn't the best it is NOT because of Kubuntu. It is because my 4060 died and I'm stuck right now on the integrated AMD video.

OVerall I've not encountered anyu issues. Things run great and I actually have no idea I'm running on new code, new kernel, new anything.

[Schwarzer Kater]

[…] I then added Flatpak (don't know why this isn't installed!!!) […]

Probably a "political" decision by Canonical.

[…] and followed all 6 steps for "After you install Kubuntu" tasks. (Interestingly they don't say you have to activate a Firewall!) […]

I suppose you are talking about a firewall between the internet and your home network/private desktop PC here.
Most routers for the consumer market already have a decent build-in firewall that is turned on by default nowadays (like - to name one example - in the Fritz!Boxes that are very common here in Germany for 90% of private internet connections).

You can of course additionally activate a firewall in your desktop Linux (like for KDE Plasma 6.6.x in -> System Settings -> Wi-Fi & Internet (section: Networking) -> Firewall ) or take other measures.
In most cases it won't make much of a difference if there already is an up-to-date firewall running on your router - also depending on the configurations and your individual use case, of course.
An additional firewall can generally be useful if you connect to the internet with an old router that has not received firmware updates/security updates by the manufacturer for some time to close specific security vulnerabilities or if you connect to the internet by other means, though.

That are reasons why I would activate a firewall on a case by case basis and not by default for a desktop installation (behind a modern router).

[Qqmike]

I think of things this way:
Modern routers incorporate NAT, Network Address Translation -- a networking feature, not a firewall.

As Gemini puts it, to paraphrase...
Your ISP gives you a single public IP address. Inside your home, your router gives every device a hidden, private IP address.
NAT translates your private internal IP addresses to your single public IP address when sending data out to the web.
The Security Benefit: NAT acts as a one-way translator, it creates a natural barrier.
It ensures that unsolicited incoming traffic from the internet cannot reach your internal devices, because the outside world doesn't know your internal IP addresses.

It would seem to me that that alone would more than suffice for most casual users, and for many not-so-casual users.

I've heard of it but haven't studied it, but since we're here, allow me to drop a concluding tidbit from Gemini in case it's helpful:
"Most consumer routers today combine both technologies [NAT + Firewall] into what is commonly known as an SPI (Stateful Packet Inspection) Firewall working in tandem with NAT."

[Schwarzer Kater]

As an example a brief description of the build-in firewall of one of the current VDSL Fritz!Box routers (and of course it uses NAT):
https://fritz.com/en/apps/knowledge-...-the-FRITZ-Box