As with everything, trust is required eventually. It’s more about reducing the amount of trust required than removing it entirely. It’s the same with HTTPS - website certificates only work if you trust the root certificate authorities, for example. Root manufacturer keys may only be certified if they have passed some level of trust with the root authority/authorities. Proving that trust is well-founded is more a physical issue than an algorithmic one. As it is with root CAs it may involve physical cybersecurity audits, etc.