~20 mins before, all was well. I was using Mac Chrome with an infinite number of windows and tabs. Mac Chrome was running for several weeks. Separately, there is a Safari browser (covered) with only a few tabs and a Brave browser (covered). Brave browser has only one window with a few tabs, but its focused on a googledocs editing-page with over 200 pages.
: it's covered by other windows. In other words, effectively "minimized", but not minimized to taskbar. (I wonder what's the right word for this?) Yea, Mac is weird.
Now, Mac Chrome crashes when I tried to up-zoom the page google-image-search using ctrl-+.
After Mac Chrome crashed, it asked me if I wanted to restore and I click OK, but it did not restore using the correct user-data-dir but a separate user-data-dir which crashed months ago (Fucking hell, chrome phail!). And while I let Mac Chrome months-ago-user-data-dir to restore, letting it run for ~10 minutes, I sense trouble and quit the running Brave-Browser, which quitted successfully.
Now, after Brave-Browser quitted, I Ctrl-Q quit Mac Chrome months-ago-user-data-dir. While its quitting, I browse using Safari. Now, while browsing Safari, Mac Chrome months-ago-user-data-dir crashed while its trying to quit (Chrome phail!). And shortly after, Safari give me the problem stated in this question.
(I suspect it's the Brave browser or Mac Chrome that did something to hang the Mac input system.)