How do SAE J3061 and SAE 21434 relate?
SAE 21434 is intended to cancel and supersede SAE J3061. J3061 related security and safety processes to each other. The SAE 21434 security process is decoupled from safety. On first sight, the higher-level security process of the two standards is mainly compatible. SAE 21434 is more opinionated on the workproducts that arise as part of the Threat Analysis and Risk Assessment (TARA) though.
J3061 just introduces various TARA-methods in Appendix A so that readers could pick what fits their needs best. The result of the TARA are the Highest Risk Potential Threats, which is where the methods join the common process and have Cybersecurity Goals formulated based on them.
Since the SAE21434 is a joined development with the ISO, it is also published as ISO21434.