There are very specific reasons why stuff was moved, rearranged, etc. Actions were duplicated or removed to the top menu to arrange them on different mental models - task, function, etc. So the “Window” menu is now used to bring up any information/panel from a single place, organized by category. So where previously something like “performance diagnostics” (which sees maybe 0.1% of users activate per day) no longer has an inscrutable “chiclet” button on the view tab but a named menu item. Same with things like microprofiler or network stats which more often than not came up because someone accidentally hit the emacs-like keystroke chord rather than intentionally loaded it. So there was a specific goal of decluttering the tabs for niche actions.
Now, of course someone might make regular use of performance diagnostics, or in your example the collapse/expand button. Do you care that it wasn’t reached for very often? Should you? Of course not, it was something that was a convenience for you. And that is totally fine!. I’ve said this before on other threads on this topic, but there is no possible way we’d get this perfectly right for any one user. I appreciate the acknowledgement that the old UI wasn’t perfect – there’s a lot not to love! – and neither is this one!
That’s why custom tabs exist, and so much of this was built around the custom tab concept. You can add that expand/collapse button right back into the tab of your choice in seconds. You can fine tune to the exact layout you want.
And if you want something closer to old layout, check out this project by @TenebrisNoctua mentioned earlier in the thread.