It seems like the Probuilder Vertex Color tool is still deprecated, and in the forum I found online, the Unity Technologist has suggested to use Polybrush instead. https://forum.unity.com/threads/probuilder-has-no-vertex-color-painting-options-where-are-they.670033/ Anyone also encountered this issue? and any workaround?
Vertex Color is deprecated on Probuilder, which means it is not supported anymore and won’t be in the future. The easiest alternative is Polybrush as suggested in the thread you shared.