Summary

The narrator hotkey cannot be rebound or disabled. It does not appear in the key binding interface.

What I expected to happen

I expected to be able to rebind the narrator toggle hotkey or disable the narrator activation entirely.

What happened

Without fail, the narrator hotkey toggles the narrator.  There is no option to disable, nor is there a configurable hotkey.

Why this matters

violine1101 points out:

This key not being able to be rebound is a huge accessibility issue in itself; on some keyboard layouts, some letters are written by pressing Alt Gr (which acts as if you would press Ctrl and Alt simultaneously) and another key at the same time. For instance, to write the at symbol @ on a German keyboard, we need to press AltGr + Q.

Now, on some keyboard layouts, some letters or symbols are written by pressing AltGr + B, which will toggle the narrator in Minecraft. For instance, if you're using a Polish, Hungarian, Czech, Slovak, or South Slavic Latin keyboard layout and want to write the symbol "{", you need to press exactly that combination of keys.

for myself:

One of my favorite things about Minecraft is the rich ecosystem of mods.  Some of the most popular mods are forced into awkward keybindings because of this issue.

How to fix it

Look at this comment by geni for a concise explanation including source code references.

https://bugs.mojang.com/browse/MC-122645?focusedCommentId=547830&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-547830 

Instead of checking for the hotkey in this hardcoded way, it just needs to be handled the same way as (almost) every other keystroke in the game.