The WebAnimationsCompositeOperationsEnabled flag has been on by default for well over a year and serves no purpose at this point.
Pull request: https://github.com/WebKit/WebKit/pull/19159
Committed 269452@main (bfe384e8cb75): <https://commits.webkit.org/269452@main> Reviewed commits have been landed. Closing PR #19159 and removing active labels.
<rdar://problem/117118536>