House Of Leaves was published in 2000 and Backrooms originates (as far as I can tell) from like 2011? Not that it's impossible that the ideas developed independently, but given how big a cult hit House of Leaves was I'd be very surprised if there wasn't some direct lineage. Not trying to gatekeep, it's just that the Backroom trailer was giving me _really distinct_ HoL vibes. I wonder if that's just the film mixing in ideas that weren't necessarily present in the original copypasta.

edit: Another thing I will say is that I've noticed both HoL and Backrooms seem to act like a kind of shibboleth for a particular demographic (not even really the same demographic) and you often see this in how people write/talk about both. I think it maybe stems from how dense/unapproachable the two works are, how innocuous they seem on the surface such that you really have to sink some effort to get at them.