At the moment, the only way the copilot can be disabled is via the MSFS 2024 'Pilot Profile > Customise Identity' settings. Those settings can be accessed by clicking on your Xbox gamertag when in the MSFS 2024 main menu.
We have less control over the pilot characters in 2024 compared to the avatars in 2020, so unfortunately, there are some limitations currently compared to their functionality in 2020. Hopefully, that will improve in future sim updates, or we will be able to find an alternative workaround.
Mark - Just Flight