BautAufWasEuchAufbaut

This isn't the point of the review. Verified apps only say this is the application as offered by the original vendor.
If the original vendor were to bundle malware, then that's a bad vendor, but still verified official software. Not that I actually think this will happen. Most user install malware such as Discord willingly. /j

Sleeping on it: major version upgrades. In Debian there's no automatic way to do it as far as I know?
For people with little technical experience, this could be a substantial hurdle or even problem.

I am strictly speaking about user experience here. If something goes wrong with snaps, solutions are harder to find than traditional ways of installing software. I don't think most users care about the underlying systems otherwise.

https://isopenbsdsecu.re/
I don't think much changed since then, but would love to be proven wrong.

I feel like that might be Debian stable now? With Ubuntu adopting snaps and Debian containing firmware in the installation iso.

And why does Apple's process say something about Flathubs process?

For Flathub there are verified apps though, which are confirmed to be by the original developer.

It is not convenience, it's being able to use a device at all in some cases. In others, firmware (updates) contain vital security and stability fixes.
I agree that proprietary software should not exist. I just think that the way you advocate treating firmware harms that goal.

As freeware or free software? Because if it was freeware, I don't understand how OpenBSD could have forked it

But then the proprietary firmware is in the device. Why do you think it makes a difference if you load it at boot time?
It just restricts your options.

Also if you care about security, install goddamn firmware updates. The firmware on the devices is only going to get more insecure. If the company wanted to insert a backdoor, they have done it already. If an attacker wants to attack your device, an outdated device is simpler to compromise using publicly available info than to go the expensive route through the manufacturer. The first doesn't even need to be a nation state adversary.
If you want to protect yourself against rogue devices, IOMMU and microkernels are a better and more sensible solution.

People like me can't change what big companies do. They just do it, and get their money from other companies and consumers who don't care.
I personally don't want to watch while free operating systems become increasingly unusable and insecure. Let's instead use the devices to our advantage as much as possible.