Undo can be turned on from the 3DO menu. It can be set to a reasonable number depending on your machines available memory. The option can be found under Painting>Performance. Please see attached image.
Undo has been disabled to assist with performance on larger textures (8K +) as a lot is required from SUITE when dealing with large texture formats, disabling it improves performance.
Tags: 3DO, Painting, Undo, Activate, Enable, UI, Performance