A office 365 offline installer is a nice thing to have.
Nice for the customer that might have a slow internet connection on the one hand.
And on the other hand nice to have included in a base image that you can roll out to new devices.

I want to give you a short rundown on how to create one.
Download the Office Deployment Tool.

Then go to config.office.com and create a configuration XML.
You can define settings like the installed office language, license, processor architecture etc.

Once you have turned all the switches and knobs the way you want then, you can export this into a XML file.

Start a CMD and run the setup.exe (Office Deployment Tool) with the parameter /download <Path to the XML file>.

This will download a Folder “Office” to the location of the Setup.exe
Copy that folder and the setup.exe into the same folder on the target machine and run the setup.exe with the parameter /configure <Path to the XML file>.

This will start a offline Office installation.