Can I set up Cubase Elements 9.5 so that the bar lines from the Project Window and the Key Editor are perfectly aligned with each other, and that they stay aligned, even if I zoom in or out, or hit “play”?
In my current set-up only the cursors (in “stationary cursor” mode) are aligned with each other.
Use the ‘Link Project and Lower Zone Editor cursors’ button in the Lower Zone Key editor toolbar (not sure this is available in Cubase Elements).
Oeps, it’s actually in the Manual …
I see, that’s not the manual for Elements 9.5 
That’s why I hate these “product differentiation” marketing ploys. In the old days, companies would have their decent, fully functioning base package and then start adding bells and whistles for the more expensive “pro” version. Now, they also start with the base package, but delete some essential parts from it, and then call the base package the “pro” version, so that they can suddenly charge triple for it. In the mean time you pay what is still good money for what is basically a dysfunctional version.
This bar alignment thing is a good example. It’s such an essential part of music editing software that it was probably in there from the very start of Cubase, when there was only one package. Now you suddenly have to pay serious money for it. It’s like a car model that has been selling well for ages, suddenly being sold with the wheels as an expensive option. You didn’t raise your price, did you? Or did you? Being the trusting loser I am I bought that car I always knew to be a good car, only to discover afterwards it doesn’t come with wheels anylonger. I can’t resell it, so in the end I’ll have to pay up for the wheels. Nice move, guys.
The link you’ve given is the Link to Cubase Elements 9.5. Whether this feature is actually in Elements 9.5 and the manual is wrong I don’t know as I possess 9.5 Pro and Elements 9.
Cubase Elements has always been a different software to Pro and Artist (which are the same executable), there have been different versions of the software since the very early years.
The bar alignment is a new feature. Indeed it can only have existed since the introduction of the lower zone which came with Cubase 9 (2016) since before the Lower Zone there was nothing to align with.
Well, what’s for sure is that the PDF version of the Elements 9.5 manual doesn’t feature it, and I can’t find it either in the software itself.
Anyway, if that’s all for “dysfunctionality”, I can live with it. 
It wouldn’t be the first error in the Elements manual.
The feature is not in Elements.