@jcurrie94 to add an excel file to all items in a list at the same time you would be best to use a simple flow in Power Automate. The overall flow looks like this:
In the get items action, if you have more than 100 items in your list you will need to click the 3 dots at the top right of the action, and select settings. In the screen that opens turn on the pagination toggle and set the threshold to more than the number of items in your list.
The get file content using path actin is the location in OneDrive for Business where your excel spreadsheet is stored.
Then add an apply to each, select value from the dynamic content box then add an add attachment action:
Rob
Los Gallardos
Microsoft Power Automate Community Super User