why is that and how can enable it, win 10 64, 4k monitor. thx
That is because, in the Page Editor, The View is set to "All Images" and they are already being seen in HQ.
See first screen shot below.
Set the View to "Thumbs/Small Images" and HQ View will be active. It's faster to work in this mode too as changes to crop etc. are seen much more quickly.
See second screen shot below.
Terry
PS. if you put Context Sensitive Help ON in the Help menu, then you'll see a brief explanation.