where is 'bootstrap'? can't install CMake

Question

I want to install CMake on my server with linux OS. But I can't find any 'bootstrap' file, so can't install it for 3 hours. I want to go next step,, please help me. what's wrong with these step? (see below)

1. I downloaded 'cmake-3.28.1-linux-x86_64.tar.gz' <- My status: Ubuntu 20.04
2. I upzipped it
3. As far as I know, the next step is:

cd ./cmake-3.28.1/
./configure --qt-gui
./bootstrap && make -j8 && make install -j8
#./bootstrap --prefix=/usr && make && sudo make install

in the above line, I went to next step by substituting ./configure~ with _configure~ but when I went to the next line, I got error like this:

zsh: no such file or directory: ./bootstrap

I know that there is no bootstrap folder or file in my cmake-3.28.1 directory. I looked around many posts about installing CMake, so I found that I couldn't go next step unless I resolve that 'Bootstrap' line.

Has anyone experienced same situations??