I am merging 2 legacy microsoft applications in modernization project. One is CMS site running on SharePoint 2013 and other is .NET 2.0 web application having transactional UI functionality. I am in favor of a common JavaScript UI portal (ReactJS) and access the backend (including SharePoint 2019) through REST APIs sitting behind an API Gateway. Alternate solution is use SharePoint Framework (SPFx) but then frontend will become tightly coupled with SharePoint and also require converting to SAML 1.1 for authentication. With first approach, my architecture will be simpler and flexible to upgrade UI in future.
My question is - can I use on-premise SharePoint 2019 server just as CMS through its APIs? If yes, are there reference architecture available? Any guidance will be much appreciated. Many thanks.