Unrealized and Closed P&L for futures contracts are calculated using the same formula as inverse perpetual contracts. For a detailed understanding of how both P&Ls are derived, please refer to the following article

P&L calculations (Inverse)

By default, all closing of futures position(s) before the settlement date will be based on the Last Traded Price (LTP) on Bybit.

If the position is left open, at 08:00:00 UTC on the settlement date, the system will automatically settle the open futures position(s). However, instead of using the best bid/ask prices inside the order book, the settlement price will be determined by averaging the index price every second from 07:30:00 UTC to 08:00:00 UTC. For more information, please refer to Index Price (Futures Contracts)