The only thing I can think of is that the keyboard isn't set to English UK. Mouse to top right select the search icon. Type Language in the search bar and select settings. Select 'add a language'. The pane that opens should show English UK. If not click on the blue 'options' to the right, then click on 'add an input method', scroll to English UK, click on it select add. The pane that then opens gives you the choice to remove other input keyboards.
OnePlus 5T review: Hands-on