I am planning to customize the Addins option(Right-click on Table object) and trying to find SysContextMenu in D365 F&O but I don't see its available. Does anybody know whether this feature changed in D365 F&O? How can I customize or extend the standard right-click Addins option?
Yes, it has changed. Development is now done in a completely different software: Visual Studio instead of the AX client application. The old solution is not applicable to Visual Studio; you must develop Visual Studio add-ins instead.
Start by creating a new project in Visual Studio and choosing Dynamics 365 > Developer Tools Addin template.
Unfortunately there is no comprehensive documentation, but you can get inspiration from a few existing projects, such as D365FONinjaDevTools.