office 365 and office 2019 : Microsoft Office 2019 is known as the latest version of Microsoft Office. Similarly, Microsoft Office 365 is a web-based version that Microsoft prefers users to adopt. Microsoft Office 365 stands out from older editions of MS Office is that it integrates all the aspects of the apps with the cloud. It is a subscription service that means users need to pay a monthly or yearly fee to use it.
The previous version of MS Office, including Office 2016, didn’t offer all of the cloud features that Office 365 does and is not a subscription. Office 2019 is a one-time purchase just as other editions were like office 2016. Office 2019 is one-time purchases are available for both PCs and Macs. Furthermore, no upgradation means if you are planning to upgrade to the next major release, you’ll have to buy it at full price.
With Office 365, you get extra online storage and cloud-connected features that let you collaborate on files in real-time. You can always have the latest features, fixes, and security updates along with ongoing tech support at no extra cost with a subscription.
Office 365 Home plan makes you share your subscription. You can share it with your family for up to 6 people and use your apps on multiple PCs, Macs, tablets, and phones.
Therefore, Office 2019 and Office 365 are entirely different from each other. One can choose it according to their need and purpose.
source : office.com/setup