Thanks. Terminate and resetting didn't work but using the photos legacy app as default photo viewer opens the image fully.
The default Photos app remains broken as is, opened images open in the background and "Open" image from right click menu is still in the wrong place.(unless that was just part of a windows update I'm not aware of?)
I even uninstalled the Photos app and "Open" was at the top again in the correct place in the right click menu. Re-installing Photos from the microsoft store fresh and the problem comes back. I guess I'll just be using the legacy viewer from now on then heh.