I'll answer this one myself. Below are done in Excel 2016

Workbooks.Open ("/Users/OldAl/Desktop/OldExcelTest.xlsm") 'Opens Dialog to Open WB
Workbooks.Open ("/Users/OldAl/Desktop/quotes.csv") 'Works - Opens the .csv file
It seems .csv files open directly and .xlsm files get the dialog box

if workbooks are in the same place/folder
Workbooks.Open (ThisWorkbook.Path & "/quotes.csv") 'Works Opens the .csv file
Workbooks.Open (ThisWorkbook.Path & ":quotes.csv") 'Doesn't Work - gets "Can't Find..."

It's the last one that is in all my Mac Excel 2011 Workbooks. It looks like they missed the fact that Macs are different in describing Paths. Ugh! I didn't figure out how to open an .xlsm file directly without going thru the dialog box. It seems that in some of my attempts it happened but not reliably.