Yes that's what Intel has been preaching for 2 decades now, but I don't believe it, if it were true, then how come Intel could not compete spending more than Arms entire revenue for 10 years to try to make a better CPU than Arm? They failed for 10 years with $10 billion in losses trying, and then they simply gave up, because they were basically no closer after 10 years than they started out with. And that was back when they still had a production process advantage!!!

But apart from that AMD would make an Arm CPU because it's become a huge ecosystem competitive in scope to X86. AND I have zero doubt that if they do, they will prove to have better power efficiency than their X86 offerings.
AMD was at it before, but that was when they were near bankrupt, now AMD is hugely profitable, and can easily afford the extra R&D, but of course they will only do it, if they believe they can capture Arm marketshare enough for it to be profitable.

Internally, AMD got pretty far along in making an ARM architecture called K12, but it got scrapped because they didn't have the money to make two architectures, so they focused on Zen.

And AMD is likely working on ARM stuff right now.

Reportedly, they recently restarted their efforts on an ARM SoC design in order to try to get Nintendo to switch (heh) to them for the Switch 2. Nintendo stuck with Nvidia because they could guarantee 100% backwards compatibility with the Switch and AMD couldn't.

Again reportedly, AMD didn't shut their new ARM group after this, seeing that Microsoft is opening up Windows to non-Qualcomm ARM SoCs (believe it or not, MS did give Qualcomm an exclusivity deal for Windows on ARM). AMD wants in on that before others take up a piece of that pie.