The macos split puts both windows necessarily into fullscreen-mode, thus raising the issue of that mode being escaped when pressing, well, 'escape'. The issue arises in them handling the windowing differently. So I would argue the windows aero-snap-feature and the macos fullscreen-split-feature are more use-case congruent.
Also, a fullscreen application in windows cannot share the display as a macos fullscreen application can.
Furthermore, I'm of the opinion that the app generallyl emphasizes keyboard-only navigation too little, hence the confusion in tabbing hierarchies however, that is a different matter windows, the fullscreen mode is - in my opinion - for more cumbersome than the keyboard oriented aero-snap feature. I still feel that, generally, the use of escape to leave fullscreen mode - especially in a textual environment - is an anti-pattern. But when sorting, and working with notes on long-form writing, I have scrivener together with evernote on one space. I also have vim and hyper bindings active, which will leave me in a tiny minority. Just fyi: for quick note-taking I mostly use geeknote from the terminal, browser clips or the quicknote-feature - which I love. Thus, I'm left trying to relearn my decades old vi pattern of pressing escape before navigating in the editor. I have tried application specific key-redirection using karabiner, but the escape will still registers. It needs to be stated, that using 'escape' to leave fullscreen-mode is a standard darwin behaviour, that can be disabled by application developers. So, to be clear - having tested retrospectively whether the 'escape' key leaves fullscreen mode in any permutation of selections of panes and/or elements: yes it does - this only happens in the macos version of the desktop client. I also don't understand what you are trying to tell me. I am, however, basing my thinking that the screenshots of yours are of the web version on my client looking significantly different.
Was of the opinion that posting this in the Evernote-for-mac-board, mentioned issues will pertain to the desktop version only.