Yes, it is still supported.
From time to time there are breaking changes like the new possibility to encrypt all communication to and from Recording Server introduced with XProtect 2019R1, but in general you will be able to use MIP SDK based application on “future” versions of the VMS.
See this explanation. https://developer.milestonesys.com/s/article/about-MIP-SDK-compatibility-with-XProtect-product-versions