Feedback is often extremely neglected, and expectations can often be set poorly.

Telling an engineer you expect literally 20% of their time to go to their mentee, not 20% of their free time, but 20% of their total time seems like an important expectation to set.

Applying major pressure to mentors to write consistent thoughtful honest required feedback is probably the best thing to do. Like minimum 3 paragraphs per week, potentially with direct prompts for questions people would prefer not to give direct feedback for.

Specific choice of project can also make a big difference.

They don't have one at my company. Are this actually common? It seems everything out of HR's mouth today is to the tune of "you hold the power to guide your own career and self-learn".