In BC Saas, the object range [50.000..99.999] is free. That means you can use the development environment, VSCode, to create apps (extensions) that can create new objects, like: tables, pages, reports, codeunits, xmlports, queries, profiles, enums,...
Via table-extension and page-extension objects you can make, limited, modifications to existing tables and pages, from the base app.
You can not modify reports, only create new report objects, but in one of the next releases there will be a new object type: report extension, that will allow you to make, limited, modifications to report datasets.
Object Ranges - Business Central | Microsoft Docs:
docs.microsoft.com/.../devenv-object-ranges
(+) Which object ranges can we use with Microsoft Dynamics 365 Business Central? - Dynamics 365 Business Central Community:
community.dynamics.com/.../which-object-ranges-can-we-use-with-microsoft-dynamics-365-business-central
Overview of Dynamics 365 Business Central 2021 release wave 1 | Microsoft Docs:
docs.microsoft.com/.../
