The following post contains a simple picture of what is described in @rfeigel’s post
As a further note, are each of the flows appending different tabs on the Excel file?
If so, you could potentially use a single Excel Writer, and create multiple input ports (one for each tab)
Alternatively, if they aren’t writing to multiple tabs, you could do similar with a Concatenate node prior to the Excel Writer, and have that feed into the single Excel Writer node.
