to provide a visual guidance(applicable to QGIS version 3.10.1-A:)
- Navigate to Layer --> Save As
- On the Format dropdown, select 'comma Separated Value [CSV]'
- Provide the filename to save to
- In the lower section, expand 'Layer Options' if not expanded (scroll down if required
- Select 'AS_WKT' for 'Geometry'
- Click OK