Many people who don't know what they're talking about in this thread. No, used memory does not include cached memory. You can confirm this trivially by running free -m and adding up the numbers (used + cached + free = total). Used memory can not be reclaimed until the process holding it frees it or dies. Not all cached memory can be reclaimed either, which is why the kernel reports an estimate of available memory. That's the number that really matters, because aside from some edges cases that's the number that determines whether you're out of memory or not.

Anyway the fact that you can't run Linux with 16GB is weird and indicates that some software you are using has a RAM leak (a Firefox extension perhaps?). Firefox will use memory if it's there but it's designed to cope with low memory as well, it just unloads tabs quicker so you have to reload often. There are also extensions that make tab unloading more aggressive, maybe that would help - especially if there's memory pressure from other processes too.

Pano perhaps? It doesn't show up at the cursor but you can search in it, the keyboard works the way you would expect and it auto inserts on selection.

Running poweroff is one of the correct ways on anything Systemd (details). If that doesn't work then something is broken.

If you haven't done so already try looking into the journal. sudo journalctl -b -1 -e will take you to the end of the log for the last boot.

Yeah some people seem to have this expectation that there should just magically be a button to unbreak the PC. They talk about their personal pain points when using Linux as if there's a conspiracy of devs to hide the unbreak buttons for the sake of elitism, but that... just isn't a thing? If it was that easy to fix an issue, you probably wouldn't need to fix it because the system would already come unbroken by default. I sympathize with everyone's Bluetooth configuration woes but mostly it's a pain in the ass because Bluetooth, in general, is a pain in the ass, not because of elitist devs (who I should mention are doing this in their free time for no pay. There's almost no money in desktop Linux, unlike in servers).

It doesn't help that US diverging diamonds seem to insist on having pedestrians walk through the median.

But honestly all interchanges are varying degrees of horrible and if you want your city to be bearable to navigate as a pedestrian/cyclist you just really don't want to do urban highways, or roads above a certain size in general.