"Additionally, with the ECH extension not yet being widely used [17], [71] and focusing on privacy protection rather than censorship circumvention [60], it can be censored easily by blocking it entirely [14], [76]."
The paper describes various GFW bypass methods that currently work, including removing the SNI extension entirely
It does not mention anyone using ECH to bypass GFW
Perhaps it is too early to conclude "China blocks ECH" because ECH is not in widespread use
