In Writer's Tool -> Customize... dialog, Keyboard tab (making sure "Writer" is selected instead of "LibreOffice"), the "Shortcut keys" box shows all the available keyboard shortcuts.
Corresponding Shift+Backspace (one can press Shift+Backspace combination when the focus is in the "Shortcut keys" box, or just simply scroll down to its place) entry, the place where an LO function is supposed to be, shows an useless "Shift+Backspace".
While Shift+Backspace is special in other modules (e.g., it undos selection in Calc), it doesn't seem to do anything special in Writer, and just works like Backspace. If indeed Shift+Backspace is not used in Writer, this entry should be cleared and left empty.
My "About LO" information:
Version: 220.127.116.11 (x64)
Build ID: f82ddfca21ebc1e222a662a32b25c0c9d20169ee
CPU threads: 2; OS: Windows 10.0; UI render: default; VCL: win;
Locale: zh-CN (zh_CN); UI-Language: en-US
Also reproducible in 6.3.3.
I confirm it with
Version: 18.104.22.168.alpha1 (x64)
Build ID: cc57df8f942f239d29cb575ea5a7cb01405db787
CPU threads: 4; OS: Windows 10.0 Build 18362; UI render: default; VCL: win;
Locale: de-DE (de_DE); UI-Language: en-US