What I really liked about Coherence Mode in older versions of Parallels Desktop, was that the menu bar of the host macOS was hidden.
I know it is possible to achieve that by adding the appropriate setting for LSUIPresentationMode to the info.plist inside ~/Parallels/"YourVirtualMachine".pvm/"YourVirtualMachine".app/Contents/ using Terminal:
This will add the following lines to the info.plist:
plutil -insert LSUIPresentationMode -float 3 ~/Parallels/"YourVirtualMachine".pvm/"YourVirtualMachine".app/Contents/info.plist
It also keeps the host's Dock out of the way so it doesn't open when hovering over it.
However, unlike older versions of Parallels Desktop, in present ones there is no way to get the guest's menu bar in place of the host's menu bar. That is, (with described addition to the info.plist) instead of the host's menu bar, with a height of 23 px a "bar" with the host's desktop background is shown. And right under that the guest's menu bar is displayed.
Though clicking on that empty "desktop bar" may be used as a way to bring one back to the host system, that also happens when clicking the guest's menu bar and missing it by just a px or more. Now as moving the cursor to the very top of the screen and clicking the menu bar is something very natural and done quite frequently, this behaviour is very annoying as it disrupts the workflow.
I know that making the menu bar invisible and allowing an application (in this case a Parallels VM) to use its space, in older macOS versions could easily be achieved by editing the info.plist, while Apple removed that possibility from newer macOS versions. However, I also know that it is still possible to achieve that behaviour by implementing it in the program's code before compilation.
Therefore I'd very much appreciate if you'd re-add this functionality in future versions of Parallels Desktop. For macOS guests, that would be very helpful.