Looking for anime (pre-2021) – people trapped in huge indoor area, each has own small house

Hi, I’m looking for an anime I watched on YouTube before 2021.

What I remember:

• It had a modern anime style (around 2014–2018)
• Small group (about 6–10 people), normal humans from the modern world
• They were trapped, starting in a dark room, trying to escape
• Later they were in a huge enclosed area / hall, possibly with a simulated sun
• Inside was a grassy open field, very few paths
• Each person had their own small house, houses facing each other
• There was a sand area (like a playground), rest was grass
• Day/night cycle, daytime looked colorful and almost friendly
• No school setting, no fantasy world
• Psychological / survival / experiment vibe
• Very few episodes (short series or OVA)
• One person was found dead outside later (possibly hanging, not 100% sure)
• After everything, survivors may have returned to normal life

I watched it on YouTube, possibly a short anime, OVA, or web anime.

Does anyone recognize this?