Is there a way to set Libre office Calc to launch when another program requests to launch excel by default?
It depends on what way an another program launch an Excel.
It may be hardcoded. The question seems to be more complex.
@njg010259 The part: “…when another program requests…” in your question is confusing me.
If you want LibO Calc to start when you click or double click and Excel file, you need to go to
LibO / Tools / Options / Load/Save / Microsoft Office the (L) column for Excel.
If you like to have all MS Office files opened by default by LibO, check all fields there. ( I have all checked.)