My claim was that there where computers where Linux only ran with Microsofts signature. I listed two systems (HP/Surface) where this is the case. Mainly because finding more is a pain, with support requests more likely to go off to nowhere instead of outright showing that no support for it exists.

One might make the case that Microsoft claimed it would require the ability to add alternative keys and conveniently failed to enforce that claim. If the goal was to blame Microsoft instead of just showing that Secure Boot can be easily used to lock users into one top down approved system.