This article covers MPLS and Packet-Mode support in MPLS
Is MPLS and packet-mode supported on SRX4600?
Based on the following documentation, both Packet-Mode and MPLS are not supported SRX4600:
https://apps.juniper.net/feature-explorer/feature-info.html?fKey=3696&fn=Packet-based+forwarding+and+security+features%3A+Forwarding+option%3A+packet+mode
https://apps.juniper.net/feature-explorer/feature-info.html?fKey=6444&fn=Interface%20family%20-%20mpls