This example it work

`${site url}/_api/lists/getbytitle('${Title Name}')/items?$select=File/Length&$expand=File`

I get data from Document library

But I'm using in the latest SharePoint online, I'm not sure it would work on the old version

This example should work:

${site url}/_api/lists/getbytitle('${Title Name}')/items?$select=File/Length&$expand=File

I can get data from Document library.

Note: I'm using the SharePoint online site, I'm not sure if it would work on the old version.