The only thing that Office online can be used for in any reliable sense of the word, is view only content. Even then you might find that if the source is a Word doc in a browser and the target is any other form or rich editor- you get what you pay for. I'd like to see Microsoft focus on bringing me desktop apps built in native code for the platform that I'm working on.
Here's what Office Online or Office for the Web or Microsoft365 Online, or whatever it is called has brought us. A software as a service with a never-ending subscription which Microsoft then uses to replace full-featured desktop versions of their software, like Outlook, and replace it with OWA bundled up inside of a React Native wrapper pretending to be a native desktop email client. It's not native nor is it an actual email client.
I believe that if they can convince enough people that the online version of the app is nearly good enough, they'll make more cross-platform, apps with feature parity (to the web) and still bill us the price that you'd pay devs to build native applications in languages that parse and render quickly without costing 4 gigs of RAM standing still.
Can we quit pretending web toys are real software fit for productivity?