how can I find more not want limit how can change step to where ??
same window, under the System tab yoiu’ll find the Undo step setting
edit: beaten by the goorman. 
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thanks too much I use Mac mini M2. thanks. too much!!!
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hmmmm not work only 30 that all I did set 100 won’t work. will screenshot
Maybe some memories restrictions?
Try to save your preferences after you made some changes:
Or try to set Undo Memory Limit also to 100.
might also have to restart blender after you save those preferences. 
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that better clearly show full screenshot. thanks
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You may also write your settings into Startup File so that no matter what .blend file you open in the future, it will always load your saved preferences you’ve made before. At least as far as I know that.
oh I will do start again why I do make shuttle train my idea but start again. haha. ok thanks also can’t undo. more. but that fine. I will start fresh again. bummer. thanks.
There might be some restrictions due to your hardware, but I’m not sure about that
it ok alright. I just restart blender then new fresh that fine. thanks for your help. when I have some question will post thanks.
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Having 100 Undo steps will take up memory. All those Undo steps are held in memory.
If you need to go back more than 20 steps you need to learn to make duplicates as you work. Then you can go back to the duplicate if you need to.
I have a collection called Bkup when I work. It is turned off in the outliner so nothing is visible. As I work and get to different stages I Shift-D Duplicate the mesh and move it into the Bkup collection. If I make a big error and need to go back, I can go grab any of the stages. No need for 1,000,000 Undo steps.
Good luck.
got it thanks for clarify