In general, the "onboarding" I have seen for non-trad hires and new grads at several companies has been absolutely non-existent... they pair these newbies with senior devs who either spend a lot of hours per week pairing and mentoring, or they ignore their mentees who then typically flounder.
It's an enormous wasted opportunity. A proper onboarding curriculum has a tremendous return on investment. While perhaps impossible to measure, you can't tell me that it's not easily 10x or something like that.
I am more of a traditional SWE, not an SRE, so I can't comment on this one directly. But in general, more of this.