A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data.
You have "fixedwidth.txt" which, say, has a couple of dozen columns with a fixed width and a total width of 1000 characters. You want to import that into Excel as a couple of dozen columns.
Start Excel (on the mac), go to File / Import (forget the pointless ribbon, use the proper application menu bar) and click import. On the dialog select Text file and click Import. Select fixedwidth.txt, brings up the "Text import wizard"
Select Fixed width. Next >.
Now try and select one of the right-hand columns off off the "preview of selected data" canvas. You can't. It won't scroll *sideways* with the mouse. Only way to scroll it sideways is to change my Mac's settings because Excel's broken.
Click Apple / System preferences / General / Show scroll bars. Select "Always".
Go back to Excel. Alas it's still broken. So Cancel the Text import wizard.
Back to the File / Import / Text file / select file... Text import wizard now has a scroll handle enabling you to scroll sideways. Still won't scroll sideways with the mouse (because it's broken).
Now fiddle with the column widths as required and import the file.
Then reset your Mac's settings back to the way that works with all other applications (except Excel's Text import wizard).
HTH