Help, saved game disappeared

@LILBRO2KBABY  Downloading a Gallery item creates several files, but none of them are the same format as a save or land in the saves folder, so they therefore wouldn't overwrite your save.  I do wonder though if part of the problem is that your OneDrive storage is full.  You should be able to see free and total storage somwhere within OneDrive; I'm not exactly sure where because I don't use it.  This is not about the space on your internal drive(s) but rather the space Microsoft provides to free accounts.

For the save itself, if you place it in the location where your other saves are, in this case:

C:\Users\anneb\OneDrive\Documents\Electronic Arts\The Sims 4\saves\Slot_00000006.save

(as you said before), AND the save has the correct file format, you should be able to load it from the Main Menu.  The correct format is Slot_ followed by an eight-digit hexadecimal number, with a .save extension, and no other extraneous characters.  For example, if your save file was labeled Slot_00000002 1.save for some reason, you'd need to delete the 1 and the space in front of it.

There is absolutely an easier way to go about this, in fact more than one if you want.  Personally, I might consider creating a new Windows account.   You'd be able to move over your data from the current account, and you could set it up so OneDrive isn't interfering.  You may be able to fix the settings in your current account as well, but the problem is that Sims 4 is already reading the OneDrive folder by default, so things could get a bit more complicated.  But it's a viable option too.  Let me know if you're interested in either one.

The reason I keep mentioning it is because OneDrive can keep causing problems when it's allowed to sync your user files.  Even if you resolve things now, you might run into the same issue down the road, so it's best to find a more permanent workaround.