If you just want a faster, more stable experience on an old device, staying on 9.3.5 (or using a lightweight jailbreak) is often better than going back to 8.4.1.
After downgrading, you will not be able to restore a backup made from iOS 9.x or newer. You’ll set up as a new device. Also, iCloud services and app compatibility will be very limited. downgrade ios 9.3.5 to ios 8.4.1
Downgrading from iOS 9.3.5 to iOS 8.4.1 is technically possible only on certain 32-bit devices (iPhone 4s, iPad 2, iPad 3, iPad mini 1, and iPod touch 5th generation). This is because Apple still signs OTA (Over-The-Air) updates for iOS 6.1.3 on iPhone 4s and iOS 8.4.1 on other listed devices, allowing a downgrade trick. If you just want a faster, more stable