Selection.

How do I get, as earlier, the end of selection to be the end of the track by default? And now it’s 0.

To extend a selection from the cursor position, or to extend a selection, to the end of the track: Shift + K
To extend a selection from the cursor position, or to extend a selection, to the end of the project (all tracks): Shift + End

For other selection shortcuts, see: http://manual.audacityteam.org/man/audacity_selection.html

Thank you!

Although, you can press the right arrow. But I asked that the end of the track should be the default, there’s nothing to press.

I’m not sure what you are trying to say. To move the cursor to the end, press the “End” key or the “Skip to End” button