New to SharePoint

Hi Handel10

I believe Microsoft would point you at the Power Platform (Apps / Flow / BI) as the initial solution for replicating your workflows in M365. 

Most of my SME clients make use of the standard power platform functionality included with Microsoft 365 licenses, but stop short at purchasing Power Apps or Power Automate licenses which would provide access to premium connectors for their users. You can get a lot done with standard functionality, but may find you run into problems as soon as you need to call any external APIs without purchasing Power Apps/Automate licenses.

There is a DB2 connector you might be able to use (DB2 - Connectors | Microsoft Docs). This is a premium connector so would require a Power Apps or Power Automate license for each user making use of the connector.

If purchasing Power Apps/Automate licenses is not appropriate then you could create your own Web API as a wrapper around your DB2 database to perform your CRUD operations. You can host the Web API in Azure (Functions / Logic Apps / App Service) or in your own infrastructure. You can also use Azure AD to control access to your API.

You could then use SPFx to build webparts, extensions or commands which make the HTTP request to call your API.

Generally I would recommend doing as much as you can in the Power Platform as it is a (little) bit more accessible to non-developers, but recognise when your workflows are getting too complex to be reasonably maintained in that environment. When that happens, switch to SPFx and make use of your own Web APIs.

SPFx also has the benefit of integrating with Teams, meaning you can create webparts which can be used as Personal Applications or Teams Tabs.