Turns out the amd machine had huge tables enabled and after disabling those the regression was there on and too. So arm vs amd was a red herring.

Of course not a nice regression but you should not run PostgreSQL on large servers without huge pages enabled so thud regression will only hurt people who have a bad configuration. That said I think these bad configurations are common out there, especially in containerized environments where the one running PostgreSQL may not have the ability to enable huge pages.