Well hidden in the delete menu, there was a checkbox among many others that I automatically clicked - an option to delete saved site passwords.
Oh boy, was this a fatal move?
Soon thereafter I got the answer to that question. All my passwords from Google Password Manager were deleted and this new state was synced across all my active connected Google devices.
Is it possible to make such a serious mistake when deleting browser history? Google says it is. And there is no (easy) way back. Thinking about replacing your separate password manager with Google Password Manager? Well, think again. What's Google's response to this situation? Silence.
[If you're lucky, a possible remedy: Find another connected device that hasn't been synced with the new state yet. Ensure the sync doesn't activate on it (disable the internet connection on the device). Export the saved passwords. Sync the device. Import the previously exported passwords. Sync again.]