Welcome to the forum!
The "Linked Image Not Found" big red X image indicates that one imported raster image is not showing. The most likely reason for that, is that you must have moved the original to a new folder (in Windows Explorer), or less likely, you deleted it. Or possibly you have opened the SVG file on a different computer from where you have the image. It just means that Inkscape can't find it anymore. So unless you deleted it from your computer, it's not lost. You just need to find it, and either re-import it, or re-link it. Or embed it, so that it can't get lost.
For the drawings which are missing, the location of those is not so certain. If you're using layers (as in Layers menu > Layers) it's possible you accidentally hid a layer....or maybe made a layer transparent. Beyond that, the possibilities are too numerous to guess about. But if you can share the SVG file, we can look around for the contents.
If it is or was a very large file, it's possible it became corrupted. Usually when we see this, nothing is really lost, but it's just some part of the code which creates the image is either missing, or scrambled. There's a....I don't know, I'd guess a 50/50 chance that could be fixed - if that's the problem. But again, if you could share the SVG file with us, we can investigate.
I can't think of any reason why having upgraded to a new version of Inkscape would have affected whether drawing contents are showing. I don't think that would be part of this problem.
