Catalina works well for me, installed in November 2019 on a new machine. I keep an install of Mojave for software compatibility reasons. I believe it’s just in a separate APFS container, the setup described in an Apple’s guide.

There were initially some issues with excess resource use by some system process relating to text input, fans spinning and all. This seems to be gone for a while now.

Two-screen setup with Sidecar is worth it!