Not sure what happened to my catalogue and photos after a recent prompted update

Hi community,

I am quite confused and can't even recall 100% what happened. The issue is that I can't find all images I had worked on previously in Lightroom Classic and am not sure how to retrieve the work of perhaps one or two years.

I have done some Lightroom courses, followed the workflow and thought I do the right thing, however I wonder if I've done something completely wrong over the last years in terms of catalogues and backups. I have never figured out how the syncing works between desktop, tablet and phone but that's a different question.

I often have my desktop open and don't shut it down. Whenever I close Lightroom, usually a question pops up if I want to do a backup of the catalogue which I always do. However, I haven't closed it for a long time so haven't done this step for a while and was editing away. I have been using smart collections and find they are a really helpful tool to create selections when edtiting and curating photos.

Recently I was wondering why for some older photos the original wasn't found anymore, but I didn't need them at that time and worked on newer ones just fine.

Then some window popped up regarding a Lightroom update and I thought I should do that so followed the prompts. I can't recall exactly what happened. I thought it was both an update of Lightroom as such and also a backup of the catalogue. I believe it was updated to the cloud in OneDrive but am not sure.

During the update a window popped up displaying "your catalog will be upgraded in order to access the latest changes in this newer version of Lightroom Classics". I had a weird feeling and took a screenshot I emailed myself, see attached.

Weirdly enough when I now open Lightroom Classic , I have only a very small amount of smart collections, and in the left pane, the G harddrive is not displayed where I had worked with for the last year or two. I was able to import a folder of the G hard drive I wanted to work with again, however I can't see any history in the develop mode for individual photos, only the "finished" photo. Weirdly enough, some have still ratings. And the few smart collections I can see are usesell as no photos can be found. 

I don't know what to do and how to retrieve my work from the last 1-2 years. Can anyone put me in the right direction, please? 

Thanks in advance!