Fully remote setups only work if they are truly fully remote, and if the seniors have the decency to research how to better handle the thing.

Onboarding can be done remote, but the best is to schedule extensive meetings / pair programming, or even just a virtual room where the newbie can work independently but ask the senior "as in the office". Or even very clear directions on when to reach out if nothing else is possible.

What happens instead that the newbie is expected to handle all the responsibility of reaching out, and when that inevitably fails the conclusion that's reached is that wfh is not for onboarding.