A “typical” home user, whom I assume is less knowledgeable about technology, is probably the person who would benefit the most from strict firewalls installed on their device. Such an individual assumedly doesn’t have the prerequisite knowledge, or awareness required to adequately gauge the threats on their network.
They also would not realistically be doing anything that would cause open ports on their machine to serve data to some external application. It's not like someone can just "hack" your computer by picking a random port and weaseling their way in. They have to have some exploitable mechanism on the machine that serves data in a way that's insecure.
Would this not be adequate rationale for having contingencies, i.e. firewalls? A risk/threat needn’t only be an external malicious actor. One’s own mistakes could certainly be interpreted as a potential threat, and are, therefore, worthy of mitigation.
I am assuming that there's a hierarchy of needs in terms of maintaining any Linux system. Whenever you learn how to use something (and you would have to learn how to use a firewall), you are sacrificing time and energy that would be spent learning something else. Knowing how your package manager works, or how to use systemctl, or understanding your file system structure, or any number of pieces of fundamental Linux knowledge is, for a less technically sophisticated user, going to do comparatively more to guarantee the longevity and health of their system than learning how to use a firewall, which is something capable of severely negatively impacting your user experience if you misconfigure it. In other words: don't mess around with a firewall if you don't know what you're doing. Use your time learning other things first if you're a not technically sophisticated user. I also don't exactly know what "mistakes" you'd be mitigating by installing a firewall if you aren't binding processes to those ports (something a novice user should not be doing anyway).
Well, no, not necessarily. It’s important to understand what the purpose of the firewall is. If a device can potentially become an attack vector, it’s important to take precautions against that – you’d want to secure other devices on the network in the off chance that it does become compromised, or secure that very device to limit the potential damage that it could inflict.
You just wrote that "One’s own mistakes could certainly be interpreted as a potential threat, and are, therefore, worthy of mitigation." The best way of mitigating mistakes is by not making them in the first place, or creating a scenario in which you could potentially make them. Prevention is always better than cure. You should never open ports on your local network. Ever. I don't care if you have firewalls on everything down to your smart thermostat - if you need to expose locally hosted services you should be maintaining a cloud VM or similar cloud based service that forwards connections to the desired service on your internal network via a VPN like Tailscale. Or, even better, just put Tailscale's service on whatever machine you're using that needs access to your personal network. And, yes, if you're doing things like that, you would also want robust firewall protections everywhere. But the firewall simply isn't ever "enough."
Anyway, just my 2 cents. The more you know and do, the greater steps you should take to protect yourself. For someone who knows very little, the most important thing that can help them is knowing more, and there is a hierarchy of learning that will take them from "knowing little" to "knowing much," but they shouldn't/don't need to concern themselves with certain mechanisms before they know enough to reliably use them or mitigate their own mistakes. That said, if you are a new user, you're probably installing a linux distro that already comes with its own preconfigured firewall that's already running and you just don't know about it. In which case, moot point. If you're not, though, I'm assuming your goal is learning linux stuff, in which case, I've gone into that.