Microsoft has officially retired support for these versions, meaning they no longer receive security updates. Microsoft Learn
LibreOffice is open-source, completely free, and looks very similar to older versions of Office (classic menus and toolbars). Microsoft Office 2010 Free Download For Mac Os Sierra
So realistically, Sierra users are locked out of recent Microsoft Office versions except the discontinued Office 2016. Microsoft has officially retired support for these versions,
– none of these are Office 2010, but they open and save Office files. Microsoft Office 2010 Free Download For Mac Os Sierra
Your best (and safe) options are: