JS nullish coalescing assignment is not support edge version 109.0.1474.0 and throw error Unexpected token '?'

Question

when i run this code in edge v109.0.1474.0，I got error message “SyntaxError: Unexpected token '?'”，it's support in 109.*，but error in v109.0.1474.0

window.xss ??= a.xss;