Having worked in a mobile manufacturer in the past close to the tech service responsible colleague, I can tell you that you should have NO trust to the service

Having worked in a mobile manufacturer in the past close to the tech service responsible colleague, I can tell you that you should have NO trust to the service center agents with your personal data. At the same time - disclaimer my personal experience only - for repairs like screen replacement, unless the agent has really f* up there is non need for any repairs extensive tests that require full device access. Since then and while I’ve been away fro the field for too many years, in such repairs I ask that they don’t reset the device and get no complaints, maybe some typical “we might not be able to ensure proper operation otherwise” which I dismiss without issues. Again my personal experience AND no iPhones so I don’t know what apple does like maybe parts pairing that needs full access or something