Suggest Painter make available a history panel (like Photoshop) that displays each item done.
Why? Because hard to guess how many un-do's or re-do's via keyboard shortcuts. And working from the menu...the info is there but only one item at a time. Too tedious to manage a list from current limited info.
The history list could be simply the menu as a longer list; say last 20 steps...or make it an option for user choice of how many steps to show.
Or could be a panel with adjustable height so user can reveal a long or short list.
The data is already available in a list....only need to code how to display; and making a menu list longer is easy peasy.
Would make user effort for undo and redo much easier.
Corel Paint Shop Pro has a History Panel. Can't be that hard for Painter to do, as well as updating and improving their selection tools.