I agree, as much as I hate Reddit’s leadership and a lot of the toxicity of the hivemind, it will be a long time before anything reaches the level of niche communities it has with a critical mass of users and I miss some of them.
Sometimes you just want to geek out about something small with the 40 people across the planet that actually care about it.
Just hold your ground and keep reading your book, eating alone etc. If someone enters personal territory, shut it down by being honest “I don’t want to talk about that” and move on. Resist peer pressure and be who you are, it’s the same as it was in school.
Also, talk to your coworkers (I know it’s hard) about whether they think it’s appropriate. You have an impression they’re on board with this level of “intimacy” but it’s possible they are just going along to get along.
If persisting doesn’t work then it’s probably time to find another job. Plenty of workplaces out there that just want you to do your job and no more.
HR is definitely not on your side either, unless you can point to specific violations of policy. They exist specifically to cover their own ass, not to actually make your life better.