UEFI secure boot on PCs, yes for the most part. A lot of mobile platforms just never supported this. It's not a myth.
Note that the comment you replied to does not even mention phones. Locked down Secure Boot on UEFI is not uncommon on mobile platforms, such as x86-64 tablets.
UEFI secure boot on PCs, yes for the most part. A lot of mobile platforms just never supported this. It's not a myth.