One of the funniest changes that came with this is that, even when everyone is working in the office now, we still communicate primarily through our WFH chat program because it is less intrusive.
It's also very handy for referring back to later — to the extent that when we do have an in-person discussion, we usually summarize it in the chat afterwards so that we can search for it in the future.
Mind you, we don't have the issues you describe (questions going unanswered for hours or not at all). With very few exceptions, such as when someone was out sick and I didn't realize, all of my questions have been answered within minutes. I imagine that is is because we are a relatively small team (albeit stretched across several timezones these days) and the chat is mostly pretty quiet.
My only complaint is that it has made the separation between work time and leisure time a lot more fuzzy. We all basically act as if we are on call all the time to answer questions, and it is common for my coworkers to even attend video call meetings from doctor's offices and overseas vacations just to say hi.
Maybe LLMs will solve this. Have them read the code and then be able to ask them questions about how it works?
It's not just docs though. Maybe it's going over an idea. "I'm thinking of solving this issue by doing X, what do you think?" Same, WFO, immediate answer. WFH, answer in 5 secs to 5hrs+ or never.
People will complain that getting a question takes them out of the zone. That might be true but it's never been true for any co-worker I've ever personally worked with. Nor with myself. It's always been easy and pleasant to answer a coworker's question. A few times a year I'm working on something so complicated I need to be uninterrupted for a few hours but that's rare, for me at least.