This can sometimes happen if the application is remembering the previous document view or workspace settings. Try resetting the workspace first, then open a new document and set it to Fit on Screen. If every new document still opens at the same tiny zoom level, resetting the app preferences would be the next thing I’d try. It may also help to mention which Adobe app and version you’re using.
Hopefully Staff or another volunteer will see this and may have ideas. For the time being, use Ctrl+1 or Ctrl+0. Let us know if any of these other threads help you.
I have looked at the same old threads. Unfortunately following the suggestions from them haven't resloved the issue for me; that's what led me to look for an up-to-date answer on here.
To add to my query. I basically just want photoshop to show an image at it’s actual size when I open it. Does anybody know the setting for this? I just thought it did this automatically like it has done for me for the last 20+ years.
That's just the zoom level — nothing is broken. New documents can open at 100% in a large window, which makes a smaller canvas look tiny, like in your screenshot.
Press Ctrl+0 (Windows) or Cmd+0 (Mac) — that's View > Fit on Screen — to fill the window with your canvas. Press Ctrl+1 / Cmd+1 for 100% (actual pixels).
More on zooming here: https://helpx.adobe.com/photoshop/using/viewing-images.html