So you tell your juniors and seniors to communicate. I'm spending some time every week talking to either juniors or peers about things they're learning. If your seniors don't initiate teaching and your juniors don't ask enough questions... That's not an issue with a remote system.

"Tell them to communicate" is much less effective than having an environment that makes it natural and encourages it. E.g. the reason way more people are fat now is not because being slim isn't possible or because willpower has gone down, its because the environment is different. You can just tell people to eat less or you can make eating healthily and less easy.

Given the state of the fresh grads and the company culture in my previous company, wfh is much worse onboarding.

"An environment that makes it natural and encourages it."

In 24 years of IT, I've never seen this unicorn environment.

My previous company managed it with the expectation that people take regular breaks and pick someone to take that break with.

I think you're probably right, although I can't shake the fact that I picked up a lot of this stuff myself or through online interactions (e.g., IRC). Given how much more software holds your hands these days I'd expect a lot of juniors bent on becoming seniors to do quite well.