This is not exactly it. What I meant was, something what IrfanView does: when you open an image (or any file the program can read), you can press a button to open the (alphabetically?) next or previous image in the same folder.
Looks like Preview only has this, when you select all files and open them (Cmd+O). Wish it was like IrfanView.
I’m confused here , so like if you’re in a folder with a file selected and hit the space bar , does pressing the arrow keys not preview the next file for you ?
I just found out by mashing all the buttons I could think of. :-)