Lightroom CC is a 1.0 version. You are going to be missing quite a few features compared to a 10 year old product like Lightroom Classic. That's only natural and maybe you should have tried Lightroom CC a while before plunging in and doing a complete migration.
I 100% agree that Lightroom CC needs multi-monitor support. Lightroom Classic is unusably slow, even on a screaming-fast brand new PC. If CC is the future, Adobe needs to migrate all key photo-editing features like dual monitor support or continue to lose their userbase to other products.