Local Photos Library needs wiped

After an upgrade to Catalina I know a bunch of my photos are no longer uploading to Icloud properly - it tells me that but doesnt identify them in the smart folder it should put them in... Ive run repair god knows how many times ..looked through all the photos but cant see any issues.

I also have an old 2011 Imac on Mjoave and it also syncs to icloud so I can see that machine has no issues with whats in Icloud and all is well there.

SO I just feel like blowing everything away on my local drive and starting again with a fresh download to my Macbook Pro ... i am however wary of just losing everything if it tries to sync an empty library.

How best to do this?

How best to achieve this?