I realized that I wasn’t getting notification sounds on incoming Teams and emails. Confirmed that Do Not Disturb is not enabled and that sound levels are all set to their normal range.
So, I thought I’d go ahead and reboot. But, holding the power button for more than a second or two just opens the Assistant ("Hi., how can I help?") and continuing to hold the power button for extended periods (30 seconds or more) still does not pop up the power menu.
Actually, further research shows that I now have to press Power and Volume Up at the same time to access the power/emergency menu. When did that change slip through?