In 1.9b3, the in-game menu doesn't work to reassign certain key bindings. Editing the raw .xml seems to be the only way to change them.

I noticed this when trying to reassign the brake key to its former place (the period key) instead of its new place (the down arrow).

Shanejfilomena brought this up on the forums on the release thread:

relanat 16 Jul 2021:

I have found that the in-game menu does work but it is finicky.
Click the desired key first, then click "Bind key to..." then the desired function.
Tedious IMO and also sometimes doesn't always 'take' and needs to be done twice to change the setting.

But as Shane said, I usually just copy the <KeyMap> section from an existing Settings.xml file.