Azure Synapse does not have exactly the same feature set as SQL Server. I don't know off-hand whether Synpase support row-level security or inline table functions.
Your question is a little funny. As long as you can create the function, why bother if you see them in Object Explorer or not. But I see that you are using SSMS 17.9.1, which is quite old. If the support for RLS was added to Synapse Dedicated Pools after SSMS 17.9.1, that could explain why you don't see it.
Try downloading and installing SSMS 18.12, https://learn.microsoft.com/en-us/sql/ssms/download-sql-server-management-studio-ssms.