Ok, so I am not an expert, and I am not the OP. But my understanding is that Secure Boot is checking with a relatively small list of trustworthy signing certificates to make sure that the OS and hardware are what they claim to be on boot. One of those certificates belongs to a Microsoft application called Shim, which can be updated regularly as new stuff comes out. And technically you can whitelist other certificates, too, but I have no idea how you might do that.
The problem is, there’s no real way to get around the reality that you’re trusting Microsoft to not be compromised, to not go evil, to not misuse their ubiquity and position of trust as a way to depress competition, etc. It’s a single point of failure that’s presents a massive and very attractive target to attackers, since it could be used to intentionally do what CrowdStrike did accidentally last week.
And it’s not necessarily proven that it can do what it claims to do, either. In fact, it might be a quixotic and ultimately impossible task to try and prevent boot attacks from UEFI.