Corrupt apple downloads!

[Cosmix]

thats true and i know, this is regular.. but unregular is other storry like hackintosh

To make a Full Installer USB (recommended ), you need a working system that could be a target for El Capitan.

May be you can get a spare PC, install a macOS, then create a Full Installer USB (chicken or egg dilemma)
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Dortania's Guide "Making the installer in Windows" is easy to follow.
What is un-clear ?

 

[Cosmix]

I should make instalation macOS: Offline Method

Yes !

.. i need usb bootable instaler and windows option is only online

On a working "modern" macOS system you can download High Sierra app.

How to download and install macOS - Apple Support

Download and install current or previous versions of the Mac operating system on compatible Mac computers.

support.apple.com

Now, using high Sierra app, create a bootable Full Installer USB ( High Sierra )

Now, find a "spare PC" (for temporary usage, say a Haswell system).
Using the USB created above, install High Sierra.

On this "spare system" download El Capitan .dmg file. Open the .dmg file and install the .pkg.
The El Capitan app should come up in /Applications folder.

... and now create a Full Installer USB for El Capitan

It seems complicated, but I find it doable.
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Otherwise, find a friend/neighbour who already has an old system (minimal High Sierra ) but not too new

Example :
Using a Sonoma system I get this message :

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Years ago, Apple sold "Mac OS X Snow Leopard" ISO kit. This was a nice starting point kit in building a hack (may be it could be used in VMs ?) and from there building new incremental installers/updates/upgrades ....
It looked like this ( just an example ) :