A mess

Some have gone to one drive

P.S. while you fix your file management mess, disassociate LrC catalog(s) from OneDrive. Some might say LrC + OneDrive, was made in Heaven, others say Hell. One way to do this is to create a new root level folder and relocate your catalog to that folder. OneDrive autosyncs various user system Libraries (folders) by default, some of these are Pictures, Videos, Music, Downloads, Documents. and user. So name that new folder something you like, that makes sense to yo, perhaps MyPhotography, MyLigitroom, MyPhotos, Rumpelstiltskin, GrumpyOldFart, anything other than Pictures, etc.

By the way, Backups????

If you describe the problem in a lot more detail, we can probably advise you on how to fix this.

Photos missing can be fixed via https://www.computer-darkroom.com/lr2_find_folder/find-folder.htm

You've to make it by yourself. Here you'll find a series of articles with informations that may help you.

Merging Catalogs - The Overview | The Lightroom Queen

Adobe does not nor are there other services that I know of.