Backrooms: Escape Together has 11 procedurally generated levels according to the game’s Xbox listing.

Quick Scoop

That means the current answer is 11 levels. The listing describes the game as a co-op horror experience where you “journey through 11 procedurally generated levels” while progressing deeper.

Small caveat

Backrooms games can change over time with updates, and one recent post also mentioned a newer added level and event, so the exact in-game content can evolve.