Hi @James_Eades,
As you correctly pointed out, there is not such specific flexible formula in Coda, for the moment.
If you think it could be somehow a useful workaround, have a look at this example:
I provided some intermediate columns just to show the output, but you basically can just keep the formula in Working Days column.
As well as - obviously - the Weekdays Pattern table (with the same logic as in Google function)
As said, it’s a workaround, but flexible enough to be quite portable in different tables.
Let me know if this helps.
Cheers!