Subscriptions for 365 across devices...?

I don't think so. I purchased my subscription directly from Microsoft so there may be a difference but I am able to use it on all devices and I note the following from their website: https://products.office.com/en-us/buy/compare-microsoft-office-products-for-mac?ms.officeurl=mac-compare-redir

(for the Office 365 Personal product)

For one person, across all your devices.

Ask Microsoft Support. Their product, their licensing, their fine print, their decision, their confusing quagmire.

Or load Apple Pages, Numbers, and Keynote—which can read and write most Office documents—and avoid the whole question.

As for your question, here’s what Microsoft has posted:

Numbers has some templates for this.

Try a Microsoft site for Word and Excel stuff...

On the other hand ...

I just went to ‎Microsoft Word on the App Store

scrolled down to "License Agreement" at the bottom of the "Information" section and clicked on that. As would be expected there is a lot of fine print legal wording but there are a number of statements there that lead me to believe that the license purchased via an iOS app is valid only for iOS devices. Following is one example from that section:

You may use and install copies of the application on an unlimited number of iOS devices you own or control subject to the service terms and conditions for the consumer subscription found at http://office.microsoft.com/office-365/FX103453735.aspx so long as you have a valid subscription license to the service.