It seems the issue is the little input sources switch in the top right in the menu bar. It's defaulting to, probably US English, which is the wrong keymap for my keyboard - should be UK English - so some of the characters in my password are being entered incorrectly.
The bug is that this is being reset on every boot. A second bug is that the recovery options thing that says I can reset the password of my account doesn't do anything.
In the meantime, I've decided to go back to macOS Sequoia. I honestly do not like Tahoe.
The corners of dialogs are too curved; same with buttons.
Dialog boxes have left-justified text, which looks messy.
The glass effect in most places makes it difficult to read the contents of the window (see the weather menu item for an example).
Because of the curves everywhere, where there's a straight line that separates some section of, say, System Settings, the two are so badly positioned that it looks absurd.
I just cannot get on with this, and doubt I'll be upgrading until I'm forced to do so.
Topic:
Community
SubTopic:
Apple Developers