A bug!

Why do the script throws can not open vendor/imgui?

[dudeawsomeness1]

Make sure you do a recursive clone, so it also clones the imgui repository:
git clone --recursive https://github.com/StudioCherno/Walnut.git

But it does not works!

[BeardyMike]

But it does not works!

Just double checking, have you followed all the steps in the readme?

It might be worth doing them all again.
I'd fully redownload and go through the install steps again.
This would be similar to "Turning it off and on again" , which really does fix a lot of IT problems.