Take an iPhone or a Switch. Then disable Secure Boot on it. Good fucking luck.

The reason why Apple or Nintendo go out of their way to make this impossible isn't user security. It's the "security" of their 30% App Store cut.

Out in the wild, Secure Boot exists to "secure" vendor revenue streams - and PCs are the only devices where it's even possible for the user to disable it. Most of the time.

What's happening in smartphone space is enough of a reason to treat Secure Boot on PC like an ongoing attack. The only reason why there are still legitimate ways to disable or adjust it is that most PC manufacturers don't have their own app store.