Up front: maybe this is something that isn't possible at all, I don't know.
I've tried Opus d8viewer.exe, XnViewMP, Faststone Viewer... no luck.
Scenario as follows:
Selecting a folder with images
Select Images tab (Style)
Sort on Modified date
Double click any image. It will show up in the associated program.
Within that program, click on [Forward]
With me, some other image will be displayed, but not the one that is displayed on screen (in the Opus right panel) as being the next.
For example: an 2018 image is displayed, the next -would- have been another 2018 image, but after 'forward' a random 2020 image is displayed, skipping the images in between.
From that point on (2020), the viewer follows the date time sequence properly.
That is with XnVIew and FastStone. D8Viewer also skips to some other image.
If Preferences / File Operations / Double-click on Files / Use internal picture viewer is on, or if you open the viewer from Opus via the Show command, then the files will be listed in the same order as the lister that launched the viewer.
Otherwise, and especially when using third party viewers, it is up to them how they sort their files.
My fault.: User internal picture viewer was set to 'unregistered picture file types'.
I went on to change filetype association ("Opens with' ) and browse/selected d8viewer.exe for .png and .jpg
Double clicking a file obviously would launch Opus viewer, but it did not follow the same sequence as shown in the right window panel.
It does so when selecting 'All recognized pictures' at Use internal picture viewer.
Super, thanks again.
I should have asked before...
BTW, whilst being happy with this solution, is there a way to send an image from within the viewer to an external program, like XnViewMP or Photoshop, so as to be able to correct colors. Some kind of 'Send to' or so.
Of course I can separately launch them and open the photos from there.