These technologies are complementary.
SIEM
It centralizes and analyzes events from numerous sources.
EDR
Primarily monitors endpoints and provides detection and response capabilities on these devices.
XDR
Seeks to correlate signals from multiple security domains, according to the provider's architecture.
SOAR
Automates security and response processes.
Therefore, we can have:
EDR → SIEM → SOAR
The EDR provides data.
The SIEM correlates and analyzes.
SOAR can automate certain actions.