How to add tree prefabs when editing terrain in Unity?

Question

Unity

Switched to version 2020.3.17 from 2019.
Adding prefabs to Paint Trees Terrain does not work. You click on the Edit Trees -> Add Tree button and nothing. The screen flashes and everything, no window with the addition appears. I thought that the matter was in the downloaded prefabs (quite old), but I don’t see the prefab created from the standard 3D Object either. The project rebooted and even created a new one - no reaction.
What am I doing wrong? Maybe they came up with a new mechanism, but I don’t know?