iOS apps cannot add systemwide actions in context menus, like for text selection. At best, they can create a sharing extension to have their app shown in the share sheet (page where you select who you send something to) and potentially add an action for easier discovery.
The only place they can add a systemwide actions is in their own app, hence why only the ChatGPT app has the Ask ChatGPT action.
Technical explanation:
iOS apps cannot add systemwide actions in context menus, like for text selection. At best, they can create a sharing extension to have their app shown in the share sheet (page where you select who you send something to) and potentially add an action for easier discovery.
The only place they can add a systemwide actions is in their own app, hence why only the ChatGPT app has the Ask ChatGPT action.