I rebind the key for the boost to a different key and it remains bound to that key. However, upon closing the game and relaunching it, the key will be reset back to the default (B).
Steps to repeat:

• Launch the game
• Go into the settings
• Open Controls and then click Key Binds
• Find the button for the Immersive Aircraft boost key.
• Rebind it to a button of your choosing
• Exit the settings menu
• close the game and then relaunch it
• Reopen settings menu -> controls and check key binds again
• Key should be reset back to its default.

How to do that? I cant config the mod ingame

Pretty sure same happens with dismount button.

Turn off useCustomKeybindSystem in the config, next version will do that automatically on forge.

Debugging help is welcome here btw.

I have the same issue, but for every keybind. They all reset to default