Is there a way to get UNDO HISTORY to stay open in its own window?
No. They really should add that.
Damn. I came here to ask the same question, and there is no such feature? This is really inconvenient. I cannot really easily notice what I have undone by pressing Ctrl+Z multiple times, and even the names on the pop-up undo history menu are not very helpful.
Blender should have something like this that Krita has… Do similar competition 3D software, like Maya or something, also lack this feature?
I don’t think I’ve ever seen something like this apart from 2D software. Most other 3D DCCs have a form of proceduralism that make this kind of undo history mostly irrelevant, but in Blender it would be welcome. As for the question of accessibility, you could always make an addon that replicates the list and displays it in the sidebar.
Modo’s had this for years. https://www.youtube.com/watch?v=pZF4rAijOOU
Granted I know nothing about Modo
Well, somebody else suggest it to TPTB: they’re tired of hearing me.