Hmm, not sure then. It might be called something different. But I do know exactly the thing you mean from having it on my work computers, and I find it very annoying, too.
Veraxis
I believe some Dells have a bios setting for dynamic brightness which can be turned off.
I am a big fan of Zero Japan's teapots. Glazed ceramic, and i have put them in the dishwasher for years with no issues. I think they also go by the name Bee House. The infuser they come with is pretty good, but it turns our that the mouth is also the perfect size for a Finum medium basket strainer.
Gesundheit
Detecting and setting up printers
Do you know the specs of this laptop off hand? 2007 would place it in sort of a grey area between 32 bit and 64 bit CPUs. If it is 32-bit, you are likely going to have major issues and I would recommend using something else.
Even if it is a 64-bit CPU, the performance may not be amazing, and running modern browsers with anything less than, say, 4GB RAM could be an issue.
I would recommend something lightweight, such as Linux Mint with the XFCE Desktop Environment. You may need to get even more aggressive about finding something lightweight for something that old, though.
I have been using KDE on Arch across several machines for about 3 years now, then Manjaro for a year before that. At no point have I experienced instability or issues like that. Especially that last one; I'm the sort of person who regularly has 10+ tabs open on laptops with a fraction the amount of RAM that you have.
I would say that is definitely not normal. If that happened to me, I might search online or check journalctl -b -p 3 to see if it yields any clues.
I've literally never heard of Bodhi Linux, but apparently it is a fork of Ubuntu LTS, which will have very outdated packages if that is a concern for you.
AntiX is likewise a fork of Debian Stable, so I suspect it will have the same issue. It also does not use the more standard systemd init system, so finding support could be an issue.
I don't think that it make sense to start off on such obscure distros. The advantage of a widely-used distro is that there will be forum threads and a much larger network of support to help you learn and debug issues.
I can't really speak to the security aspects of either X11 or Wayland.
XFCE is probably a good, lightweight DE. Many distros will support it. I believe Linux Mint has an XFCE version by default. I'm sure they will get to Wayland eventually, but it sounds many of the features will not matter to you beyond just a working desktop.
I have never tried it myself, but maybe Debian with XFCE might be more lightweight than Mint? Probably more involved to set up, though, so I would research that a bit more before taking the advice of a rando who has never done that specific distro/DE combination.
How so? I have never found installing yay difficult, and using it is essentially the same as pacman with the addition of aur packages. What issues have you run into?
ClamAV

But on a serious note, no, I have no idea why that would happen.

Every few days on the machines I use daily, but I have a couple spare laptops which I only use infrequently, and I usually don't run into any major problems when I have to make a big set of updates on a machine I am using for the first time in a few months.