I want to export the data from a network call to an excel sheet with multiple tabs. Will this be considered in memory or an I/O process
I just checked out a library to handle Excel data, which is able to run in the browser (https://github.com/SheetJS/sheetjs). As the browser has no access to the file-system, the operations have to be done in-memory. If you are using this library in node, it will probably be the same.
Save and Read operations are of course IO operations, other than that, they should be in-memory.