Web Protection in Defender on Android v17 (Samsung S25) keeps switching off

You have already disabled several battery-saving features, and Defender’s absence from Never sleeping apps means the Android 13 walkthrough does not map cleanly to your S25. The important diagnostic is whether Android revokes Defender’s Accessibility permission when web protection stops. Microsoft documents that permission as essential to Android web protection and identifies background app termination as one possible trigger. Immediately after the next failure, check Defender’s Accessibility service and its own warning, then note whether reopening Defender restores protection. In the app’s information/battery settings, check unrestricted battery use and background activity if those controls are available; I cannot confirm their exact One UI 9 location from Microsoft’s published instructions. Do not assume the greyed-out unused-app setting is the cause when it is already off. Send Microsoft support your existing version details, failure time and before/after permission screenshots, and ask Samsung for the equivalent per-app background controls on One UI 9.