That missing percentage slider is definitely confusing, Saikat, but it vanishes for a very specific reason. Because you are running Windows 11 Version 25H2, Microsoft has completely swapped out the old "Battery Saver" code for a new architecture called "Energy Saver". Instead of waiting for your laptop to drop to a specific battery percentage, this new system constantly and dynamically throttles background threads behind the scenes to maximize your AMD Ryzen 7 chip. Since it's designed to run continuously rather than kick in at a set limit, Microsoft intentionally removed the threshold dropdown from this main settings screen.
If you still want that classic automated control back, you can easily bypass this screen and hardcode your preferred percentage threshold through the legacy menus. Just press Windows Key + R, type control powercfg.cpl, and hit Enter. Click Change plan settings next to your active power plan, go to Change advanced power settings, and expand the Battery option at the very bottom. From there, you can manually type your target number (like 20%) right into the Low battery level rule to force the automation back on track!