It does not look like WebKit actually supported this property: https://github.com/WebKit/WebKit/blob/3c46119f53450bbe2474543a21f78b7b24b28fec/Source/WebCore/Modules/cookie-store/CookieListItem.idl Some attributes were removed in https://github.com/WebKit/WebKit/commit/5bc8fcb69ca17d5ca4f35d609458f1998fc54cb4#diff-a7335011060fa569843009f0d02165f8fe51ff95268f9a2625cc97af4a799f7d, but `partition` was not part of the original set: https://github.com/WebKit/WebKit/commit/6178f6321703c1007f79e9beeef8d27f8da9eec2#diff-a7335011060fa569843009f0d02165f8fe51ff95268f9a2625cc97af4a799f7d _Originally posted by @caugner in https://github.com/mdn/browser-compat-data/pull/29809#discussion_r3498603565_
It does not look like WebKit actually supported this property:
https://github.com/WebKit/WebKit/blob/3c46119f53450bbe2474543a21f78b7b24b28fec/Source/WebCore/Modules/cookie-store/CookieListItem.idl
Some attributes were removed in WebKit/WebKit@5bc8fcb#diff-a7335011060fa569843009f0d02165f8fe51ff95268f9a2625cc97af4a799f7d, but
partitionwas not part of the original set: WebKit/WebKit@6178f63#diff-a7335011060fa569843009f0d02165f8fe51ff95268f9a2625cc97af4a799f7dOriginally posted by @caugner in #29809 (comment)