Where the switch lives
File → Options / Settings → Save (wording varies by EXE vs UWP vs Mac). Set Writer to DOCX, Spreadsheet to XLSX, Presentation to PPTX. Apply to new files. Old .wps files stay .wps until you Save As.
Why people forget
A teacher sends “submit as Word.” A student saves .wps because the dialog offered it first. The portal rejects it. The student thinks WPS is incompatible. It was a default. After you change it, create a new file and glance at the title bar / Save As dialog to confirm.
Compatibility mode
Saving as DOC (the 97–2003 binary) is for a museum colleague. It strips features. Prefer DOCX. If they are on Word 2007, DOCX still wins. If they are on a feature phone, send PDF.
Convert the pile you already have
Search the disk for *.wps *.et *.dps. Open each, Save As Microsoft format, keep the original in an _old_native folder for a month. Then stop. Do this on a weekend, not during the upload to the portal.
Company templates
If legal sends a DOTX, save your letters as DOCX from that template. Changing the global default does not rewrite the template’s idea of a format. Test File → New from that template once after you change settings.