What people get from a custom Windows build is a clean install that comes up already quiet. You can have that from genuine Windows: this page makes the answer file Windows setup reads, so a fresh install skips the account, licence and privacy screens, makes a local account, and leaves the free look on the desktop. Then the tune does the rest, with an undo, on Windows that still gets every update.
Everything below stays in this page. The file never names a disk: setup still asks where to install, so it cannot wipe the wrong drive.
Read it before you use it. Every line is standard Windows setup; the comment at the top says what it does.
Back up anything you want to keep first: a clean install is clean.
Microsoft's own Media Creation Tool (search "download Windows 11" on microsoft.com) makes a bootable USB stick from genuine Windows. Pick the same language you picked above.
Copy autounattend.xml to the top of the stick, next to setup.exe. The name matters: setup looks for exactly that name.
Boot from the stick. Setup asks for the edition if it cannot tell, and where to install: pick the disk yourself. If it asks for a product key, choose "I don't have a product key"; a PC that had Windows activates on its own.
No account or privacy screens: it signs in to your local account once, and the desktop has OmniDx free look. Run it to see what the tune would do on this PC, then get the tune if you want it.
A custom build is Windows with parts cut out of the image before it installs. Some of what it cuts is what keeps you safe and in your games. What they cut, and where the tune stops.
From Microsoft, unmodified, signed. Windows Update, Defender and repair from the official media all still work.
Secure Boot, TPM 2.0, memory integrity and IOMMU are untouched, which is what VALORANT and FACEIT now require.
The tune records every change and undoes it in one line; a cut image cannot put back what it never installed.
The answer file and the free look cost nothing. The tune is $19.99, once.