Help I cannot find my photos after new Lightroom upgrade

Now I see that they have a new app

So, based on the image you posted showing LrC, can I assume you actually noticed that an update to LrC was available, and you updated it?

Not a new app, but an update. Words gave meaning.

It is possible that the wrong catalog was opened when you started the new version of LrC. Perhaps an older one. The default for LrC when starting the program is to open the most previous one. But sometimes LrC gets that wrong. Sometimes after an update.

Another possibility, is you moved or renamed the correct catalog, hence LrC has no idea where the most previous catalog went, and opens a different one (LrC is not always good at error messages)

And another possibility is the preference file is corrupt.

Use Finder to look for other catalogs, they will have the extension of:

.lrcat

In addition to what dj-paige and GoldingD posted maybe this would assist. Which application are you referring to??

I have tons of albums 

Albums

as opposed to

Catalogs

First is Lightroom Desktop , current version is v4.3. Album on the Cloud

second is Lightroom Classic, current version is v10.4. Catalog on a hard drive.

What one do you have?

Now I see that they have a new app/I downloaded it

Exactly what is the EXACT name of the new software you downloaded and what version NUMBER is it?

Photos, and catalogs, do not get deleted when you download any version of Lightrrom.

If you are talking about Lightroom Classic (are you?), what has most likely happened is that the WRONG catalog file has been updated. In Lightroom Classic, use File->Open Recent and try each file listed there to see if you can find the catalog you want. If that doesn't work, use your operating system's search feature to find all files on all disks whose name ends with .LRCAT and open each file found until you open the catalog of interest.