Dear Mitsi,
Good day! Thanks for posting in the community. We are happy to help you.
According to your description, my understanding is you want to insert an Excel file into a Word online document. If so, I would like to know if you are using Word for Web to open this document, or you are using the Word desktop application to open this document.
If you are using Word for Web, it is not available to insert other files.
If you are using the Word desktop application, you can insert the Excel file as the object. Click the Insert tab> Object> select "Create from File"> Browse to select the Excel file.
When you have any updates, please feel free and come back to share with us.
Sincerely,
George | Microsoft Community Moderator