Why the permission exists
An iOS keyboard extension runs separately from its main app. Allow Full Access lets the extension use capabilities it otherwise cannot use, including reading data the main app placed in a shared app container.
The important question is what the keyboard actually does
The system permission is not a product-specific privacy statement. Before enabling a keyboard, read the developer’s privacy policy and look for a concrete explanation of what data is read, whether typed content is recorded, and whether anything is sent to a server.
BlinkPaste reads saved snippets, not ordinary typing
BlinkPaste uses Full Access so the keyboard can read the snippet library you created in the main app’s shared container. It does not record or upload what you type in other apps.
iCloud sync is optional and separate
When iCloud is available under your Apple Account, BlinkPaste can sync saved snippets and related settings between your devices using Apple’s iCloud capabilities. The keyboard’s ordinary typing content is not part of that snippet library.
A practical privacy checklist
Prefer a keyboard with a narrow purpose, a public privacy policy, clear deletion controls, and no vague claim that every permission is required. Keep sensitive or one-time information out of reusable snippets unless you are comfortable storing it in that app.