Is there any workflow builtin in this cms that can be used for content approval process?
Kirby do not offer any “out-of-the-box” solution to your question. Sorry.
The Kirby Panel (backend) does not offer this functionality.
But you can create your own UI in the “frontend” using the Users API (simply use users with Panel access for that). You can give people with permission the right to login to this system using an attribute in the user’s definition file. The actual approval process could include discussions or simply one click to publish content (by internally moving a page from a sandbox page to the final destination).
Nothing prohibits authors from directly editing the actual pages without going through this process, so that’s not useful for teams without much trust, but if everyone agrees such a process is the way to go, this can work quite well.
You could also have a field in the pages themselves:
… and restrict certain types of users from using the panel, so they have to go through your frontend UI.
And have a look at the new hooks feature which just arrived in the v2.1 release.