To remove a social channel such as LinkedIn or X from your publish options, go into any page, and click on 'Publish Options':
On this page, you'll see the "Options" section, with the possibility to fold it out on the right side:
If you have connected your account to one or more social channels, you will see 'Connected Social Media channels':
Click on 'Manage channels' to see an overview of the connected channels:
You then have the option to remove one or more channels.
If needed you can always re-authenticate with a social channel later.