Lightroom Ecosystem with Lightroom Classic

I have been using the cloud-based Lightroom for a number of months and am happy with my folder/album structure as well as the ability to edit and post from my Windows 10 laptop or my iPhone while I'm traveling. However, I've started using Lightroom Classic V12 to create slideshows, and hope to use more of its unique capabilities.

Most of my photos, including those cropped and edited, have sync'd up alright with Classic. However there are some albums which Classic says it cannot find, though it displays the photo. I've discovered several versions of the Lightroom Classic catalog with different dates on my laptop. If I were to totally uninstall Classic and get rid of the related catalogs, could I just reinstall Classic and rebuild a complete catalog?

I also read a post from a couple of years ago that Adobe recommends not trying to sync Classic with the ecosystem. Is that still the case and why?