How to make my calc template work

Having watched a tutorial (older version of Calc) - I have set a template for font and its size - but it is NOT remaining, applied. I’m on 6.2 something - newest version.

What do I need to do to make my default ‘stick’??

Any template you created must be saved before it can be used. Save it as a template (with extension .ots for spreadsheet documents) to a folder of your choice. If the extension is correctly associated with LibO you can open (“call”) it the common way (doubleclick e.g.). However, you won’t get the template opened for editing then, but created a new “Untitled” document containig what you saved to the template, in specific the redefined styles.

If you want to use a custom template as the ‘default’ you need to first import it via File > Templates > Manage Templates and then to Set as default.

Please note: There is nothing like a SheetStyle. Only the sheets already contained in the template will be shaped as you did when creating the template. Additional templates will be inserted regarding the internal defaults concerning RowHeight, ColumnWidth, and style names.