Lightroom or Lightroom Classic

Try Lightroom cloud ecosystem vs. Lightroom Classic - which do I need? | The Lightroom Queen

It depends on your main focus.

Personally, I prefer to use Lightroom Classic - A) I'm used to it, and B) it is a bit more versatile than Lightroom; Lightroom is Cloud-centric and Lightroom Classic, is locally based - images are stored locally, instead of the Cloud. This can be an advantage - especially if you want more control over where your photos are stored.  With Lightroom Classic, you have to import the photos into the catalogue, With Lightroom, they are uploaded to the Cloud and this can be an advantage.

If you want photos stored in the cloud so you view and edit them on any device, then use Lightroom. If you want to provide your own keywords, you would use Lightroom Classic.

Of course there are other differences. What differences are you concerned about? 

...when should I be using Lightroom Classic?  

By @Tezjito5

I've moved your post from Creative Cloud Desktop to LR Classic where you are more likely to get an answer to your question.

Jane