If this is of any help, 2019 is simply marketing. I've been chatting to the Mac devs for a while, "Office will be called 2019 whenever the marketing team decide to call it 2019". They have only just forked for VL and boxed versions of Office at version 16.6.2, they have released version 16.17 which has no changes in features. Office 16.17 available for O364 subscribers and is still called "2016".
This is the only official notice people had for Mac updating:
"A BIG reminder to everyone that installer divergence will occur tomorrow around ~10am. If you use macadmins.software or direct FWLink download to get your packages you need to make sure you deploy the correct version for your users. O365 activated users on macOS 10.12 and later can use 16.17 (FWLink 525133). Everyone else, including 2016 VL and O365 on 10.10/10.11 will need 16.16.2 (FWLink 871743). If you have scripts and workflows and don’t have time to implement the separation logic, stick to 16.16.2 for all users as it works for all scenarios until 9/24, when 2019 VL comes along."
There has been one major f'up with updates, from the above paragraph. 16.16 will become deactivated if upgraded to 16.17, which many people have done accidentally. When I mean many, I know of organisations with thousands of workstations. Windows requires a manual install because it uses the click-to-run installer and cannot be deployed any other way, and there is no support for terminal servers anymore so there is no easy way to get Office running. Macs are easy as you can install using a PKG, however, it is not possible to discern between what should be O365 and 2016/19 versions, and then some will only work on macOS 10.12 or later, so everyone is being kept back on 2016 if at all possible.