At least on older Macbook there's a way to override BD PROCHOT MSR setting to undo the slowdown.
I’ve got a 2017 MacBook Pro with a dead screen, dead keyboard & trackpad and no battery sitting behind my sofa, closed in a vertical stand and running macOS as a test server. Open Core Legacy Patcher will allow you to boot without the CPU slow down: https://dortania.github.io/OpenCore-Legacy-Patcher/
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