Hey there,

Unity 2019.3. is out of Beta. Seems like the Curve Editor is broken?
I tried it with Standart RP and LWRP.

Is this a known bug?

Greetings
Thomas

Works for me with Unity 2019.3.0f6 using URP and legacy 3D. If you aren't getting errors, make sure you don't have Gizmos disabled at the top of the Scene window. If disabled, it will not draw the curve editor tool.