[AnotherCat]

If my understanding is correct that from the next upgrade the intended default will be that ENTER will open a viewer for the book highlighted, then I think the following should be considered.

Is Calibre predominantly a database for managing media (books) insofar as organizing, editing (e.g. metadata), transferring to devices, etc.? If so the opening of a viewer on ENTER on a highlighted book is incorrect. Databases (and spreadsheets as has been pointed out already, do not work that way). If anything, especially another application, was to be opened ENTER typically has to select a specific field within an ALREADY opened (not just highlighted) record.

Or is Calibre primarily a media player? If it is primarily a media player then ENTER opening the highlighted media item to play (read) is correct. While a media player may allow some editing of the likes of metadata that is typically only via downloads from external servers (e.g. Gracenote in the case of music being the media) and so secondary to purpose. That said, wary users such as myself will manage media in albums or folders so that an inappropriate ENTER just takes one to the underlying list of media items rather than start playing anything. {EDIT: Windows File Explorer has been mentioned in posts, the action of ENTER on a file in Explorer is it as a player, another application will be run (e.g. an installer, text editor, spreadsheet application run - it should not to be compared to a database)}

I had understood (perhaps imagined) that Calibre was primarily a database. The evidence I see is that people use it primarily as a database and read the media on external devices. I also do not recall any significant level of difficulties experienced by users opening a viewer from Calibre (I do not recall any other than the OP) and I would have thought that "V" was obvious enough , and as has been pointed out the View menu icon dropdown list advises that.

In my view Kovid had this correct in the first place and that has withstood the test of time; what seems to me is happening now is arising out of one complaint (technically misplaced in its misunderstanding the role of standards, in my view) a problem is being created to solve a problem that did not exist for most everyone else; so is just meddling. It is not something I would allow in any applications within a configuration management system under my control (although I should qualify that by making clear that my experience is predominantly with critical systems, so meddling is never tolerated; Calibre is not critical).

But it is not under my control so what will be will be. I just wanted to state a perspective for consideration (and it may explain the wariness that seems to be in the minds of some). If I have misunderstood and ENTER will not be the default or that Calibre is actually regarded as a media (books) player, then that will not be such a diversion from practice, but, in my view, still incorrect when compared with database practice.