The Channel field values in Zoho Desk, covering options such as Email, Phone, Web, Facebook, Instagram, and X (formerly Twitter), are system-defined. These represent the actual sources a ticket can originate from, so they can't be individually removed as picklist options.
The Channel field isn't a generic custom picklist you're meant to edit; it reflects how a ticket genuinely arrived, whether via email, phone, a web form, live chat, or a social platform. Editing or removing these system values risks breaking how incoming tickets are correctly categorised, since the field's values are tied directly to Zoho Desk's channel integrations rather than being arbitrary labels.
If you don't actually use Facebook, Instagram, or X for support, you don't need to connect an account for that platform in the first place. Simply not linking a social account under Setup, then Channels, means tickets won't ever be created from that source, even though the underlying Channel field option itself remains part of the system.