apples private cloud compute can get close, its still not 100 safe because backdoors and crypto breaks are possible but you go from trusting the data center operator with all their employees to only the person thats inspecting new hardware and giving out certificates (apple in this case). if some well known non profit like mozilla or isrg starts doing it with full open source software its like the best possible security
The handy thing about trusting Apple here is: you were already trusting Apple. I don't necessarily like that trust works this way, but that's just the physics of it.