@Dharaneetharan 

you cannot generate excel as an attachment and add to record

why not use CSV?

how is your flow configured to run now?

you can use custom flow action and use script to create CSV file and then attach it to your record and then send email using Notification and in that notification use "Include attachment" checkbox

Generate CSV file through script

If my response helped please mark it correct and close the thread so that it benefits future readers.