I have enjoyed using this app because it allows the use of my license Office 365 software on Linux. I need/want to use these apps instead of the Linux alternatives because they are what is generally used in the outside world. Doing a Save As in Libre Office can mess up the formatting. The app is available in other Linux flavors and Snap, but not Flatpak or the native CL repository. Has anyone solved this problem?

Yes, indeed. Microsoft Office is standard widely used so to preserve formatting I just use Microsoft Web Apps - Office Online. Keeps formatting precisely.

I use virtualbox with windows 7, microsoft office installed (1GB RAM, 3 cpu threads). It works perfectly fine. Graphics performance is usable with guest additions installed.
I find it better than using wine or online version. Because some docx files do not render properly on the online version.