When you say that your SOT (Screen on Time) has gone down, can you share the SOT after trying the below:
1. Charge the battery to 100% & use as per your normal usage pattern
2. When the battery strength reaches 10%, go to settings = Battery => Tap on the battery icon & share the graph
3. settings => Battery => Check the screen & share the same.
Please follow below steps may improve battery backup:
1. Close apps that are not used (Bluetooth, WiFi, GPS, etc.)
2. Adjust sleep time and brightness (Settings > Display)
3. Boost memory when you see memory consumption is high with no app running,
4. check for background running applications, stop/disable unwanted apps, you can manage apps from auto-start manager.