So I decided to try James Brickley's solution. Clicked "Shut Down" from the Apple Menu, waited, first Facebook Messenger, then Mail prevented shutdown so I had to Force Quit them all (the only option other than "cancel" shown). In Safari, before I could get that message, my cursor froze and the computer would not recognize any attempted keyboard entries. Closed the lid (that sometimes works), reopened it again, but though the keyboard was backlit the screen was black. All I could do was (improperly) shut down using the power button to the right of the (useless) TouchBar. Then once it shut down, it took several presses (and a couple of minutes) and closing the lid again before the startup chime happened. (Until I heard the chime, I was afraid the computer was indeed finally a "brick"). Then a minute for the Apple Logo's reboot progress bar to load, then the usual array of user icons (nobody but me uses the computer so I don't know why they're there--maybe from previous MacBooks). Clicked on the admin icon, entered my password, and all the windows slowly reappeared one by one (including the usual "Google Drive has encountered a fatal error..." warning box--happens whenever I reboot) and I was finally able to open the PDF in Preview by clicking on it in the Downloads array.
So I didn't even get to go through the whole suggested sequence before my computer crashed. This only started being a regular occurrence in Ventura. Apple has a whole lotta "splaining to do."