I want to create custom Hub for my 4 applications where user can create request, view the request, work on assigned tasks , how can i do , please suggest me the possible approach

Create a custom Site as Hub with unified Record Type (for requests across 4 apps via relationships), Record List page (view/create), and Task Report interface (filter by app process models for assigned tasks/actions).
GO through this link for better understanding - https://docs.appian.com/suite/help/26.1/cp-13/sol-custom-suite-user-guide.html

Another approach could be to build a reusable request framework where all applications expose a common interface for creating requests, viewing details, and launching record actions. This keeps the hub generic and makes it easier to onboard additional applications without major changes.