Gallery Saves Disappeared

@AalyahReed  I think that's the issue: your other files were somehow deleted.  This is a good explanation of what you'd see under normal conditions:

https://www.carls-sims-4-guide.com/forum/index.php?topic=26535.0

Some of the files are sort of extraneous, e.g. you'd get the llama icon but the house itself would still be placeable.  But without most of the data, the game probably can't read your Tray items at all.

You may at least be able to recover some of your Library items.  Look for files that are not Blueprint files, and you may find a full or full-enough set of files for the game to read.  (In that case, please try copying those files to a new Tray folder, as described before.)

If that doesn't work, try searching your computer for the missing files.  Open a File Explorer window, click This PC in the left panel, then search for each missing file extension, e.g. *.hhi or *.sgi (with the asterisk).  If you find those files, you can add them to your current Tray folder, sort by date again, and see whether you now have a full set.  Please check in OneDrive too, that is if you use it.

Otherwise, the files you have left are unfortunately not usable, and the only thing you can really do is re-save the households and builds that exist in your current saves.

Edit:  If you can at least place the items with the flying llama icon, you can try changing one detail and re-saving them too, which should generate a new set of Tray files.