Lightroom Classic CC slow, slow, slow

An alternate way to start LR is to hold down either the CNTRL key or ALT key while you mouse click the LR icon, I always forget what key, this will start Lightroom in a mode where it asks you what catalog to open, from a list if recent catalogs. Perhaps the one you want will be listed, hopefully you did not delete it.

Now, have you attempted to reset your preference file? A corrupt preference file can lead to all sorts of issues, menu items go missing, develop tools fail, lightroom slows down, etc.

Corrupt preference files are not uncommon.

https://lightroomers.com/replacing-the-lightroom-preference-file/745/

https://www.youtube.com/watch?v=bARt-hoCc2Q

https://helpx.adobe.com/lightroom/kb/preference-file-and-other-file-locations---lightroom-6.html

https://helpx.adobe.com/lightroom/kb/recover-catalog-images-resetting-lightroom.html

at least one of those links is a bit out of date, refers to v6 preference file, as opposed to v7 preference file (LR Classic CC v8 uses a v7 preference file)

First off why do you think you must delete catalogs before uninstall LR then reinstall LR?

Second off, are these separate completely different catalogs or perhaps earlier versions of the same catalog? What are their file names? Are they in the same folder?

Not sure what you mean by LR want to update before I delete catalogs. You can't, actually there is no option to, Delete a catalog from inside LR (Or none that I have ever seen).

If you have catalog files you no longer want then use Finder, the Mac OS X File Manager, to delete them,

As for LR running slow. That happens on some systems and is usually caused by hardware or other software problems.

If you took your Mac to an Apple store to be checked out they, the so called Geniuses at the stores, only care if the computer starts up properly. If it does it is fine as far as they are concerned. So it time to start checking the hardware yourself.