This test was a failure in Safari 13, and is now timing out. https://wpt.fyi/results/intersection-observer/target-in-different-window.html?label=master&product=safari%5Bstable%5D&product=chrome%5Bexperimental%5D&product=firefox%5Bexperimental%5D&product=safari%5Bexperimental%5D
This time out makes WebKit a unique failure compared to Firefox and Chrome.
According to the test title, it seems related to bug 191558?
Safari is still timing out: https://wpt.fyi/results/intersection-observer/target-in-different-window.html?label=master&label=experimental&aligned&view=subtest&q=arget-in-different-window.html
<rdar://problem/121074518>