I didn't know that reddit subdomain. Seems to be identical to https://old.reddit.com/r/itrunsdoom/.compact

It's a shortcut to the old mobile site, yeah. "i" for iPhone. Not to be confused with i.redd.it, which hosts images.

That's just a different link to the same subreddit.

Yes, there’s a long history of it ever since the source code was either open-sourced or just made public.