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The A20 gate was deprecated (and made software-based) in Nehalem, then was removed completely in Haswell. It's never been a feature of the Zen µarch(s).

Support for the A20 gate was actually already dropped as per the article you linked:

> Intel no longer supports the A20 gate, starting with Haswell.

It was not needed anymore in Haswell, but the support was still there. It isn't supported at all anymore.

Emulation of the keyboard controller is done by the firmware. The processor's support for A20 was tied to port 92h.

The A20 line was famously used to hack the original XBox. By clearing A20, you prevent the XBox from booting from the hidden ROM, and it boots from regular flash ROM instead.

Some great videos about that on YouTube if you want to look.