When trading Options, Futures, Equity Intraday, or using Margin Trading Facility (MTF), the required margin is blocked as per the exchange. However, your available funds can still change based on your unrealised loss.
For instance, if you have ₹1,00,000 in your account and ₹80,000 is blocked for selling a lot of Nifty50 options, your available balance would be ₹20,000. If your unrealised P&L turns negative, say -₹5,000, your available balance will decrease from ₹20,000 to ₹15,000.