Going into office is one thing juniors can do about the "problem with the culture" so my stance stays the same until the so-called culture changes.
In my experience, the number of seniors who complain sbout RTO and don't hoard knowledge is tiny.
"Hoarding knowledge" makes it sound like they're intentionally trying to keep knowledge to themselves. I don't think the problem with remote leveling is due to seniors intentionally holding onto knowledge. I do see some senior employees try to hold ownership of a specific area of their work for apparently selfish reasons, but they're a minority.
I've spent a lot of time talking with other seniors (and juniors!) about ways to make sure we're spending time working with mixes of skill levels, but it's a hard problem. Just advertising that you're available to help if anyone needs anything does basically nothing to encourage most juniors to ask. It takes a lot of juniors a long time to lose inhibitions for asking for help, and I think people can often make it to senior levels without learning how to be proactive about offering help.
It does seem easier for most people to ask for help in person. I think one of the causes of this is because even in this field, most people don't grow up doing so much communication and socialization purely using crude text and video calling which have remained mostly unchanged since the 80s or 90s. Most people handle in-person socialization much better, and can read and express cues more naturally there, especially in a work environment. Also, those communication methods have a degree of formality attached to them which feels like a barrier.
Personally, I think it might help a bit if telework software would take more cues from video games (proximity-based chat and virtual environments with rooms and doors). There are some programs for this, but the few I've tried haven't been polished enough to use. The few I've used though did seem to make impromptu collaboration easier, but of course there could have been many reasons for that (e.g. novelty).