Yes, in addition to the prior zenbleed/spectre series of attacks, inception is the catchy name for the latest round of AMD focused speculative execution exploits

https://www.theregister.com/2023/08/09/amd_inception/

What you want to know is ...Who gets the least drop in performance when mitigation's are on. That is a tech blog article I am willing to pay for...

For sure. Also I remember hearing the spectre patches eventually improved (which I should check)

And what about ARM architectures? (Apple Silicon etc.)

Security through obscurity. And mac/arm users are a less valuable demographic to the writers of these exploits (for now).