Office 365 is a subscrption program, not a software product with which we can directly integrate. The customers who buy O365 can then use it in different flavor, according to their preferences (types of office: web or local installation, as well as different types of installers for the local installations: complete MSI or Click-to-Run incremental installer). Furhtermore, enterprise customers can decide which install/update channel to use, that adds another degree of freedom in the whole program. To top it all, Microsoft was changing the content of the O365 subscription during its lifetime and retains right to change it in the future (while keeping the same name of the subscription program).
For this reasons, we do cannot say apriori that we support O365, and instead we provide the list of supported Office versions here: https://help.enaio.com/redline4/admin/en/administration/installation/inst_con_systemvoraussetzungen.htm#addin
We will soon provide Add-In for Office 2019 as well. Software framework that we use for Add-In developement (https://www.add-in-express.com/) just started supporting it, so we can now rebuild the add-in and test it with this new version.